I found this on Reddit today and I think it is very good and definitely deserves to be posted where new players like me can see it. So there it is I think the review for each build analyzes (concisely) and summarizes very well most of what I've read and concluded about the same classes.
Source: https://www.reddit.com/r/Xcom/comments/ ... art_a_lw2/
I prefer these builds: Assault: Electroshock/LR - CaP - Fortifiy - Formidable - RP/CE - Untouchable - Sweeper/Lethal; Shotgun (Laser Sights, Ammo Clip) with Armor Pen Ammo, plating and vest I always considered LR to be overvalued (there's usually only one or two overwatches you have a plethora of other, safer tools to deal with, like Electroshock) and the guaranteed disorient from Electroshock is really good at shutting down dangerous abilities if your assault cannot safely kill something this turn. But I would not commit any more perks towards the stun gun. CaP is usually enough to get to 100% crit point blank if you put laser sights on your shotguns, any additional crit perks are overkill. Fortify and Formidable are IMO just too good to not take. RP vs CE is really up to the soldier's mobility. Untouchable outlcasses BeO and CCS (which requires two ammo per shot, turning it from must-pick to eh) if used correctly (if done right it essentially stuns a dangerous enemy shooter). Sweeper vs Lethal is occasional ridiculous pod-wipes vs consistency. Loadout usually a vest for HP and armor penetration ammo.
Grenadier: Sapper - HO - Formidable - HEAT - Booms - Volatile Mix/Salvo - Full Kit; SMG (Suppressor helps with their infiltration penalty), early a flashbang to break sectiod psi nonsense + explosives, mid and late burn, acid and explosive grenades; get EXO suits The environmental damage of grenades is pretty low in LW2, even with sapper you will not be able to destroy many cover objects, which is why support grenadiers with Rapid Deployment are more popular. Sapper requires you to learn which cover pieces can be destroyed at the center of the nade, however from my experience, it's enough that I prefer it over Rapid Deployment. Considering that Sting Grenades have been nerfed quite heavily (the really dangerous stuff is immune against the stun and while disorient from the flash bang disables abilities, the malus to aim doesn't matter against the ridiculous aim lategame enemies get) and that support grenadiers are mostly about the burn grenades anyway, I prefer an offensive build. That said, HO is mandatory so you get more out of the burn grenades you have to build. Again, I think Formidable is really good and it also gives the grenadiers a bit of ablative hit points since I don't give them vests, only nades. HEAT to shred more armor with explosive/acid grenades (important lategame). Burn grenades can deal quite a lot of damage with a crit from Biggest Booms, which wins out against Chain Shot (which is terrible IMO) and Sting Grenades (no flash bangs past the early game). Burn Grenades have a radius of zero (hit only the targeted tile) and one with the grenade launcher (form a cross), so Volatile Mix is nice to be able to hit grouped enemies. However, the burn isn't guaranteed, so Savlo is very nice to roll again for an important burn (or to just outright kill the target via damage), aside from the action economy it offers. While Combat Engineer and Ghost Grenade are strong contenders, Full Kit is just better, considering it gives you more acid and burn grenades and works well with Salvo.
Gunner (low aim): Grazing - Formidable - HoB - Demo - / I put low aim gunners into Havens and their perk choices are made to help them do anything. I stopped after Demo because they usually do not gain enough experience to rank any higher. The problem with Gunners in LW2 is that there is no Bullet Wizard build, they get almost no aim progression despite being completely based on shooting (even worse, their multi-shot abilities all carry aim penalties), they have an infiltration penalty and suppression is pretty bad. The suppression aim penalty is fairly small to the point of uselessness in the lategame and you do not get an opportunist overwatch shot that ignores cover when the enemy tries to run the suppression like in LW1. At least they enjoy officer training because that helps with haven advising.
Gunner (high aim): Combatives - Formidable - Shredder - Demo - Cyclic/CuP - RF/Killzone - Saturation/Fitness; Cannon (Scope/Hair Trigger, Ammo Clip, Suppressor) usually only plating and armor pen ammo with one free item slot as they tend to be quite slow It's primairly specced towards utility. You can stun mutons (not the elites, though) by standing next to them with Combatives and the 10 dodge is always nice. Shredder to, well, shred armor (you really need all the shred you can get lategame, but shredder ammo is bad as it does not scale with weapon tier like the perk does. Also, HoB isn't as good as it sounds because it eats too much ammo). At tech the build diverges based on whether your Gunner got any overwatch perks in the AWC. Cyclic wrecks MECs (really the only thing Gunners are good at), otherwise CuP for the overwatch AWC perk. Then maybe Killzone if you picked CuP, otherwise RF > Rupture. Saturation if stats are good, otherwise Combat Fitness.
Rangers (low aim): middle tree, focus on their side-arm which turns them into budget-assaults; SMG with plating and empty item slots for mobility Low aim Rangers become officers and get put into havens as advicers and train troops on easy missions using the one officer perk that auto-promotes troops. This build is actually quite potent at one-shotting two high threat enemies with Both Barrels per mission and is perfect for what I use it for. I'll even purpose train low aim high mobility rangers in the GTS for this.
Rangers (high aim): Walk Fire - Locked On - CM - Fortify - Implacable - RF - Fitness; Rifle (Scope, Ammo Clip) with plating and whatever ammo, basically I strongly dislike overwatch rangers (basically right tree with Locked On, Fortify and Fitness because Covering Fire and Suppression are terrible. In fact, Covering Fire makes overwatch rangers strictly worse) because they take too long to get going. With Sapper Grenadies, shooty rangers already get going at Lance Corporal with Walk Fire (which is really good early but kinda falls off lategame) and get a weapon tier upgrade at Sergeant with CM whereas overwatch rangers get to now crit on their single overwatch shot per turn. Fortify is too good to not take, then Implaccable allows your ranger to kill something (preferably exposed with a grenade), blue move to a flank and shoot again which becomes even stronger with RP at Gunnery. Overwatch ranger come online now but have to deal with enemy LR ruining their RR streaks. At Master Rupture is redundant with RF and Killzone with RR. If used correctly, shooty rangers are very lethal. It's always a shooty ranger that reaches Master Sergeant first in my campaigns.
Sharpshooter (low aim): middle tree with Double Tap at Master. Low aim sharpshooters get turned into holo-officers and do haven advicing, troop training and get to come support on Advent HQ assaults. Not much to be said here, it's only thing they can do with their aim.
Sharpshooter (high aim): DfA - CM - Lone Wolf - Low Profile - Aggression - Kubikuri - AMF; Sniper Rifle (Stock!, Ammo, early Scopes, later on Laser Sights), need the crit ammo for Kubikuri The DfA build is all about getting elevation and using the additional action after killing something to steady your weapon (requires you to put stocks on your sniper rifles), so the build tries to maximize the consistent one-shot potential. Kubikuri is pretty much mandatory against Sectopods and requires you to pick the crit perk on officiers and/or get mind merge on Psis if you have them so that the crit chance is 100%. Similar to rangers, having sapper grenadiers makes them come online pretty early.
Shinobi: Blademaster - Combatives - Covert - Bladestorm - Reaper - Whirlwind - Conceal; SMG (Suppressor helps) with defensive items The primary purpose of Shinobis is to stay concealed and scout. They are my primary officers which allows them to partake in fights because officer abilities do not break concealment. In case they do have to take action their sword is very potent early and midgame, though it falls off a bit lategame (shinobis should carry SMGs which isn't very good at shooting). One or two of your shinobis should pick Ghostwalker at Lance Corporal for Tower missions and HQ assaults to make sure they stay concealed throughout the mission.
Specialist: Sentinel/Protocol - Field Surgeon - Trojan - Ever Vigilant/Airdrop - CuP/Failsafe - Threat Assessment/Full Override - Capacitor Discharge; Rifle (Hair Trigger, Ammo Clip) with Plating and Skull Jack (after skull mining for the +hack), (poison/burn) ammo if mobility permits Specialist is the only class for which I haven't found a build that I consider superior to the others. I'll usually go for the overwatcher with Sentinel and Ever Vigilant because I don't build overwatch rangers since unlike rangers, overwatch specialists get going at Lance Corporal and absolutely wreck the reinforcement pods you have to deal with on the early missions. However, specialists do not have the best aim progression, hence overwatch specialists fall off lategame. Furthermore, giving up Failsafe for CuP really hurts and Airdrop is also a consideration with offensive grenadiers. Combat Protocol is also nice to one-shot drones before they get the health upgrade or to finish off low health enemies. With my other builds the overwatcher fits in better, though. With the other perks Field Surgeon is the only viable perk at Corporal as Covering Fire and Interference are trash (also, Field Surgeon is actually quite nice, as it does prevent injuries if your soldier lost only one HP, iirc). Trojan is too good to not pick as it effectively extends hacks by one turn. Its most important use is to hack patrolling solo drones as it will kill them without breaking concealment. Threat Assessment can be cast on the specialist to give him three overwatch shots a turn, otherwise Full Override allows you to hack robots. Do not get too excited though, the chance to permanently hack a MEC for the resistence is fairly low, plus it has to survive the mission to then be added to some haven, where its usefulness is limited, IMO. Tactically it is always better to go for the hack that lasts for the remainder of the mission. At Master Sergeant Restoration is a trap, the heal is pretty lackluster and it only revives unconcious units, it doesn't do anything against other forms of crowd control and it also does not stabilise units that are bleeding out. Capacitor Discharge is the only really good perk here.
Technical: FitH - Fortify - Shredder - Formidable - Incinerator - Salvo/Quickburn - Bunker Buster; SMG with plating and whatever, get EXO suits with extra rocket Technicals absolutely carry the early game. You ambush the first pod with the flamethrower, the second gets a rocket to the face which will be accurate enough with FitH. That usually leaves only one proper pod you have to deal with by other means. Fortify, Shredder and Formidable are too good to pass up, then Incinerator will upgrade your flamethrower's range which starts to be a bit too short at this point in the campaign. Salvo vs Quickburn is very much up to preference (and whether you do bring the extra rocket or more flamethrower charges). Bunker Buster is where the money is at and is pretty much the only reliable way to destroy any kind of cover; it is a sort of panic button. Also RF isn't really good with SMGs and Firestorm, while awesome, is a bit silly.
Officer perks for combat and the important missions (i.e., Shinobis): Oscar Mike - Get Some - Jammer - Collector - Fire Discipline - Infiltrator - Combined Arms Officer perks for troop training and haven advising: Focus Fire - Get Some - Trial By Fire - Lead by Example - Fire Discipline - Air Controller - Combined Arms
This was a way too long write-up off the top of my head that touches at most half regarding LW2, I guess.
Reddit user Fa1nan