The Scale

I stole the scale from Prismatic excellent Moze Skill Analysis.

The rating system used is meant to indicate general usefulness. The star ratings are by no means hard and fast rules as some skills take effort to reach their potential, and whether it is worth the effort is up to the individual.

⭐Sub-par: These are the skills that are generally bad and its really hard to make them worthwhile.

⭐⭐ Below Average: These are skills that can be useful but requires you to build around them a bit, just throwing them in to move down a tree is a usually bad idea because there are better options.

⭐⭐⭐ Average: These are the skills that are solid choices to move to the skills you really want.

⭐⭐⭐⭐ Great: These skills will make the game much easier and should be taken always if you are at that point in the tree they are located in.

⭐⭐⭐⭐⭐ Outstanding: Skills of this rating will be game changers that you base your build and play style around, they should be taken with almost every set up if you are in that tree.

Notes

Before we dive into the skills themselves, here are some things to consider:
-Rough Rider builds are popular for Zane. From my testing, Rough Rider is considered always empty and never full. There may be individual odd cases where this isn’t true, but this is the rule of thumb.

Under Cover

A slightly defense oriented tree, also focused on freezing your enemies solid, shaking off the elements, and a few shield related buffs as well.

Tier 1: Adrenaline ⭐⭐⭐

According to the math, using Barrier as an example, the regular cooldown is 28 seconds. With an additional 35% cooldown rate, it should go to 28/(1 + 0.35) = ~20 seconds, but from testing it instead is more like 7 seconds ingame. @crashc1 points out this may be a combined result from Topped Off as well, and @Superfr34k says that skill actually affects cooldown reduction, which would explain why it’s so powerful.

Skill seems to be almost worthless as of the 12th Dec Patch, as Guardian Rank skill Topped Off is incredibly strong.

Tier 1: Hearty Stock⭐

An always nice shield buff, but 3 points won’t get you out of first tier. It has come to my attention that this heavily anti-synergises with the Legendary Infiltrator, and so it unfortunately only gets 1 star.

Tier 1: Ready for Action⭐⭐

Always solid buffs. Nothing crazy. Probably the best choice to move up the tree, as none of the three Tier 1 skills do not work with RR, but this skill is useful with all other shields, so swapping off RR works.

Tier 2: Brain Freeze ⭐⭐⭐⭐⭐

This skill can effectively make any weapon cryo. Useful against almost all mobs, with only some enemies being cryo resistant or with hard to hit crit spots.

Something worth noting is that on enemies that cannot be frozen, such as bosses and anointed, I still regularly proc skills that only proc upon freezing an enemy. It seems that the game might not freeze the enemy, but you can still apply enough slowing effect to trigger skills. Still a useful skill against bosses in that regard.

This seems to be similar to Moze’s Redistribution skill: pretty much always worth the ten point investment regardless of build.

Tier 2: Stiff Upper Lip ⭐⭐

@Superfr34k says that the Damage Resistance formula is Applied Damage = (Incoming Dmg * (1 – Dmg Resist)), which is quite strong. However at higher levels damage taken is so high that 16% might not be quite noticeable. 2 stars as it can still be an extremely safe point dump.

Tier 2: Rise to the Occasion ⭐⭐⭐

Essentially a 5% health regen whilst your shield is down, which is useful on every build to help reach healthgate. The skill also even regens health when your shield is full, however the regen is extremely small.
Only issue is sharing a tier with Brain Freeze, but you will usually spec into this skill to move up the three. Solid pick, and great with a Rough Rider (RR).

Tier 3: Confident Competence ⭐⭐⭐⭐⭐

It is a cheap skill with good number bonuses, however the challenge comes in maintaining shield in order to use this effectively. As @kabflash points out, maintaining the shield and the buffs from this skill is part of the build.

Tier 4: Really Expensive Jacket ⭐⭐⭐⭐

You halve the length of status effects for 1 skill point. Incredibly useful skill for a tiny investment, and most of us at endgame are well aware of the danger of DoTs.

I haven’t tested it myself, but other threads have multiple people agreeing that 2/1 on this skill gives you a 67% reduction.

The wording heavily implies a direct reduction in time of status effects, not the “rate of which the status effects wear off”, which is how cooldown rate is determined.
E.g. -50% halves the time, and -100% means no status effects at all. In comparison to +100% cooldown rate, meaning half the cooldown time.

Tier 4: Best Served Cold ⭐⭐

BL2 AoE skills were pretty arse in general, except Bloodsplosion, but after looking at damage values in this game, I think these can be decent for mobbing.

Some unlisted benefits are that it slows enemies, and cryo enemies gain a white sheen/glow to them, drastically increasing visibility in dark environments like Eden 6. This helps me aim better, as I can make out crit spots a lot faster in the visual mess that is endgame.

A large downside is the position of this skill and the fact it does self damage. Combined with trying to maintain shields to proc Cool, Calm, and Collected, it can be detrimental.

Tier 4: Futility Belt ⭐⭐⭐

I am unsure if this is different to the Damage Resistance found in Stiff Upper Lip, but regardless 8 seconds of no DoTs is pretty good at endgame, especially for 1 point.

Something working against this skill is the fact it actually increases some elemental damage against your shield in TVHM. Unless you run a Rough Rider, this may be a detriment.

Tier 5: Refreshment ⭐⭐⭐⭐

An amazing survivability skill for any Zane who uses a cryo weapon or specs into Brain Freeze, and you really should not be this far down into the tree and not have at least 5/5 in Brain Freeze.

The reason why it isn’t 5/5 is because it takes some mild RNG and preparation, i.e. you must freeze an enemy which sometimes just doesn’t happen, and then they need enough HP to be able to survive a beating while frozen.
Squishy mobs tend to die a bit too fast to utilise this properly on M3, but this skill turns badass enemies into walking healthpacks, and on M4, I suspect this skill becomes even better.

Tier 5: Calm, Cool, and Collected ⭐⭐⭐⭐⭐

There is a certain amount of micromanagement needed to use this skill. However when combined with the barrier, it forms the basis for almost infinite skill duration.

Combined with Rise to the Occasion, you enter almost every combat encounter at full HP, so you can barrier up and get some incredibly strong action skill CD and Duration resets.

Tier 5: Nerves of Steel ⭐⭐

This skill is fairly high maintenance, as any damage will reset all stacks. However, it gives an excellent accuracy bonus. With proper management, you can get mileage out of this skill.

If the skill boosted critical damage, it could make 3, but right now it barely scrapes 2. It is pretty preferential whether you take it or not, I recommend trying for yourself and your gear.

Tier 6: Distributed Denial ⭐⭐

I am going to leave this at 2 because it just feels underwhelming for a capstone. It is definitely usable and has some neat interactions with certain shields like boosters, but doesn’t work with amp shields.

Hitman

The offensive tree, with a focus on speed, damage, kill skills, and momentum. Chock full of solid picks, a tree you can’t go wrong with. Sometimes I end up taking almost every skill.

Tier 1: Violent Speed ⭐⭐⭐

Movement speed is always nice to have and this skill helps you zip from enemy to enemy in a fight. Stacks nicely with Violent Momentum.
However, being a PvE game, the enemies aim is scarily good, so beware taking this skill won’t necessarily guarantee safety from projectiles and bullets.

Tier 1: Cold Bore ⭐⭐

With the removal of slag, swapping weapons is less critical, and the default swap speed isn’t particularly offensive. In future, with more skill points, this can be a preferential pick.
There may also be potential for some meaty damage boosts for speedkilling, with 10/5 a 60% bonus cryo damage is nothing to laught at.

Tier 1: Violent Momentum ⭐⭐⭐⭐⭐

Essentially a permanent gun damage boost, as you should always be moving around in battle. However, it can be finnicky to try go as fast as possbile to maximize the burst damage.
I am unsure if the damage scaling is linear or logarithmic, but this skill is always a good pick and will end up in most builds you make.

Tier 2: Cool Hand ⭐⭐⭐

Reload speed is always a good thing, you can never have too much. Solid pick all of the time.
I am unsure if the reload speed on kill stacks on top of the passive reload speed, or replaces it. Needs further testing.

Tier 2: Drone Delivery ⭐⭐

The SNTL drops a grenade at the beginning of it’s duration, and also 15 seconds into it, meaning at base you get 2 grenades without any duration extensions, which is alright. However if you combine Brain Freeze and Cool, Calm, and Collected, there is potential for limitless grenades and a bit of chaos.

Worthy noting that Done grenades can damage Zane. Thanks @sammantixbb for bringing that up!

Tier 2: Salvation ⭐⭐⭐⭐

Again another skill that provides something that is always useful, and this one takes less setup than Refreshment. 4 stars due to the importance of sustian in late game.
The life steal is just limited to gun damage unfortunately, as I tested and sliding, grenades, and melee did not give HP back.

Tier 3: Death Follows Close ⭐⭐⭐⭐⭐

The skill itself isn’t exciting, but it just makes keeping momentum up a whole lot easier. A no brainer, especially on M4 where time to kill skyrockets.

All skills listed in this guide assume this skill has not been chosen. If it has, all durations go to 15 seconds, and your skill tree will update to the correct values, e.g. Violent Violence 5/5 is +15 Fire Rate without Death Follows Close, and goes to +19% with it.

Tier 4: Violent Violence ⭐⭐⭐

Guess what, another solid pick. Fire rate is another great stat that could always use a buff.

Tier 4: Playing Dirty ⭐⭐⭐⭐

This skills description is quite misleading. From my testing, this is not a regular kill skill. The kill skill has a chance to proc, and that is the listed percentage chance. Once the skill procs, your next 5 shots are guaranteed to spawn another projectile.

I.e. With 5/5, every enemy you kill only has a 50% to trigger this skill. If this skill is triggered, your next 5 shots will spawn two projectiles, essentially dealing double damage.

I am unsure as to what the interaction is with shotguns/mashers.

This skill can be extremely strong but it has a lot of weird quirks, so be sure to understand what you’re getting into with this one.

Tier 5: Good Misfortune ⭐⭐

Diminishing returns is a shame, especially considering the difficulty of maintaining momentum on Mayhem 4. If you find it helps keep your skills up, go for it.

Tier 6: Seein’ Red ⭐⭐⭐

Whilst definitely a nice capstone, I find that you won’t struggle to find a small mob to kill and then get the violence started.
This is still solid for bossing however, just maybe save the skill point if you don’t plan on fighting bosses.

Doubled Agent

A tree mainly focused around buffing your clone, with a few skills promoting using two action skills.

Tier 1: Synchronicity ⭐⭐⭐⭐

Solid gun damage boost for a first tier skill. Not much else to say, other than try run 2 action skills with this skill.
Updated to four stars alongside Donnybrook, as Zane lacks a lot of damage buffs, making it more important to grab this skill at higher difficulties.

Tier 1: Praemunitus ⭐⭐⭐

I am personally a big fan of mag size increases, however being a 3 point skill isn’t great and makes moving up the tree annoying. Still a decent pick regardless if you have some spare points.

Tier 1: Borrowed Time ⭐⭐⭐

As already covered, the Brain Freeze and Cool, Calm, and Collected synergy is your basis for resetting skill durations. That being said, this skill gives a little longer to get those resets.

Tier 2: Donnybrook ⭐⭐⭐⭐

A nice gun damage boost, and another HP regen skill to make Zane even more sustainable in combat.
Not bad at all, and the fact the clone gets the bonus is icing on the cake. Updated to 4 stars on @jbow2020’s suggestion, as he pointed out that Zane lacks a lot of damage boosting skills, so taking this skill is usually a good idea.

Tier 2: Fractal Frags ⭐⭐

The skill is quite dependent on what grenade mod you are using and whether you decided to run SNTL and Delivery Drone.
There are synergies such as Quasar & Rocket launcher for easy bunching of enemies, but whether you sink the skill point is personal preference.

Worthy noting that Clone thrown grenades don’t damage Zane, and Drone throws do. Thanks @sammantixbb for bringing that up!

Tier 2: Duct Tape Mod ⭐

I enjoy this skill and think it is a lot of fun, however there are some notable downsides:
-Large magazine weapons render this a bit pointless, unless the mags take about 8 seconds to unload.
-8 second cooldown. I think the cooldown is far too long for the skill. The skill is not nearly as strong as others in the game currently, and could be a 4 or even a 5 if the cooldown was halved at least.
-Actively anti-synergises with Praemunitis
-It is a 5 skill point investment for a 20% chance.
-Choosing small mag weapons to proc grenades means more time spent in a reload animation, not shooting your weapon.

Yikes. There is just too much working against this skill. Hopefully Gearbox buffs it in future to make Zane a little more… Zany.

Tier 3: Quick Breather ?

In theory this is a cool skill, and it holds up incredibly well while leveling.
However, it is reportedly broken at the moment. When it is functional, it can be combined with Which One’s Real? and Double Barrel to give some much needed aggro relief.

Tier 4: Pocket Full of Grenades ⭐⭐

This skill is actually quite good, but it really only exists to work together with Boom. Enhance..
If you run 2 action skills and dont take Boom. Enhance., this is worthless, as it is just too deep into the tree to be really worth the regeneration.

Tier 4: Old-U ⭐⭐

Again quite a good skill, but heavily preferential. If you struggle a lot in solo play this will do you well, but if you have almost perfect gear or co-op buddies then don’t bother.

Tier 4: Supersonic Man ⭐⭐⭐

I wish the speed boost was a tiny bit higher, especially this deep into the tree. Regardless, this skill has excellent synergy with Violent Momentum, and movement speed is always welcome.

Tier 5: Like a Ghost ⭐

It unfortunately is not a kill skill and does not benefit from Death Follows Close.
The description implies additive scaling, so +6% passive bullet dodge chance, and an addition +9% per action skill, meaning that with two action skills, it goes to 24%, however this is unconfirmed.
Given 1 star as it just seems ineffective.
No dodge builds here.

Tier 5: Boom. Enhance. ⭐⭐⭐⭐⭐

A must have for clone builds. With two action skills, you’ll never be using grenades otherwise, so may as well put them to use here. By the time you are this deep into the tree this really is a no brainer for 1 point.
Synergises well with Pocket Full of Grenades, your clone will almost always be buffed with 3 grenades.

Tier 5: Trick of the Light ⭐⭐

The damage bonus is disappointing this far into the tree. On top of that, it is incredibly inconsistent in combat. Skippable skill.

It appears that the patch notes claim the values were doubled but the ingame skill description claims the above values, so I will leave the numbers as is until the ingame changes.

Tier 6: Double Barrel ⭐⭐⭐⭐⭐

Same as Boom. Enhance., this is vital to a clone build. This whole tree mostly serves to get you to these two key skills.