Original article by @Intumesce
In this guide I will go over the most useful equipment pieces, which tanks use them best, and which tier they're the most useful in. I'll rank the pieces' usefulness on a scale from 1 to 10, with 10 being the best.
Medium / Heavy / Artillery Gun Rammer - 10/10
Starting off with THE most important equipment piece, and one that is obligatory on any tank that can mount it. All tanks, save for autoloader-type tanks (with some exceptions) can mount this equipment piece. It's a 10% decrease to your reload time and a 10% increase to your damage per minute. I cannot stress how important this is for any tank type to use. Mount it no matter what your tank's rate of fire is.
Improved Ventilation Class 1 / 2 / 3 - 6/10
This is one equipment piece that's much more useful in lower tiers, which I'll get to later. The description of this item is deceiving, and makes you think you do everything 5% better. It doesn't. It makes your crew 5% better, which in turn makes everything on your tank 2.5% better. Often you can find a more suitable equipment piece to replace this, be it a Gun Laying Drive or Coated Optics, it's generally not a very important piece to have. Autoloaders can benefit from vents, since they cannot mount gun rammers.
Vertical Stabilizer Mk. 1 / 2 - 8/10
The Vertical Stabilizer (also known as vert stab or just vstab) improves your dispersion by 20% at all times. Dispersion is how big your starting reticule size is, and the smaller the dispersion value, the better. Any tank type that can mount them (tank destroyers or self-propelled guns cannot) benefit from the increase, whether they have bad aim time or bad dispersion, or good aim time and good dispersion, or anything there in-between.
Camouflage Net - 5/10
Primarily intended for tank destroyers and light tanks, it's very dependent on if you have a fully rotating turret or not in the case of tank destroyers. Light tanks, when active scouting, will make this piece useless. When passive scouting, they will rarely need any more camo than they already have.
Tank destroyers can benefit from the camo the most, but casemate tank destroyers will have to move their hull around a lot, thus resetting the 3 second timer for it to activate. Turreted tanks that don't need to turn their hull, however, can significantly benefit from this piece!
Binocular Telescope - 6/10
Binocular telescope (binocs for short) acts similar to the camo net. It takes 3 seconds after being stationary to activate, after which point your view range increases by 25%. Tank destroyers that need to move a lot will struggle to make use of it, and could make better use of coated optics sometimes. Light tanks can need the extra view range when passive scouting, though. Likewise, campy mediums might also find a use of it thanks to their good base view range and they will be stationary most of the time anyway.
Toolbox - 2/10
This is one of the many nearly useless equipment pieces on this list. Rarely will you need the 25% decreased track repair time thanks to the repair skill, plus anyone with a brain carries a repair kit to instantly repair your broken track if it's urgent. Almost any piece on this list is more useful than the toolbox.
Light / Medium / Heavy / Superheavy Spall Liner - 2/10 for the first 3 types, 4/10 for Super-heavy
Now I know what you're thinking. Heavies are prone to getting hit by arty, and reducing the damage you take from them is one the first steps to survival, am I right? Yes and no. While spall liner increases your armor versus non-penetrating HE shells and increases your crew's survivability, there's one better way of avoiding arty damage: not getting hit at all by being arty aware and looking for cover.
The first 3 types are pretty much useless as they don't give a big enough bonus, but superheavy spall liner can be considered for a few huge, slow, well armored beasts (think T95, Maus, GW E 100.)
Cyclone Filter - 3/10
Again, this equipment piece is pretty useless because it requires you to be taking damage for it to have any effect. While increasing your engine durability is nice, especially since this equipment piece is nation-specific to the Soviets, it sounds useful for those times when you take engine damage. However if your engine really is that important, just have a repair kit ready.
Fill Tanks with CO2 - 2/10
Another piece that requires you to take damage to work, this one is only remotely useful for Soviet mediums and German tanks from time to time. It decreases your fuel tank hitpoints by 50%. Yeah. Just bring a manual/automatic fire extinguisher and train firefighting if you get lit on fire too often. There's also a crew skill that increases your fuel tank hitpoints by 25%.
Wet Ammo Rack - 4/10
Probably the more useful piece among the current row of useless equipment choices, the Wet Ammo Rack (WAR for short) increases your ammo rack's durability by 50%. That is to say, your ammo rack gets 50% more hitpoints.
While a couple of tanks are prone to frequent ammo rack damage (FCM 50t, Centurion I, STB-1, just to name a few,) you will rarely have your ammo rack damaged twice in a battle if you already used a repair kit. In most cases you can just train Safe Stowage on your loader, which increases ammo rack health by 12.5% and doesn't require an equipment slot.
Coated Optics - 7/10
Very often the third equipment pick for tier 8 and above medium tanks, it increases your view range by 10%. It might not sound like a lot, but unlike binocs, it's always active! And considering the view range bar when this piece starts being useful (380m) it can bring your view range up to almost 420m on its own, which is a huge advantage when fighting low-camo tanks such as heavies.
Enhanced Gun Laying Drive - 8/10
This one is a must on tanks with long aim times, most notably self-propelled guns, some heavies, and tank destroyers. It decreases aim time by 10%. It can turn a 3.4s aim time into a 2.9s aim time. Often you won't need this piece unless you have 2.7s aim time or better. In low tiers, where vertical stabilizers are not often available, this often acts as a replacement for it.
Additional Grousers - 1/10
Probably the single worst equipment piece in the game, even worse than the toolbox, this is a nation-specific equipment piece that is only available for a few tanks even within the nation! It decreases your terrain resistance by 9.1% on soft terrain and by 4.8% on average terrain. This doesn't affect hard ground at all. It doesn't make your top speed higher, it barely helps your acceleration, and there's a crew skill that does a similar job. It might have been useful on light tanks, but no tanks past tier 6 can use it as far as I know.
Enhanced Suspension - 1/10 or 5/10
It increases your track's hitpoints by 30% and increases your load limit. The hitpoint increase is very insignificant, but to increase your load weight while grinding a stock tank in order to equip a module that would be too heavy with the stock tracks, it's really useful. When not helping you put on a heavy module, however, it's got little to no purpose at all.
Now I've covered all the equipment in the game. I ranked optics, vertical stabilizers, gun laying drives, and rammers really high. Most tank builds by good players always incorporate 2 of these on any given tank.
But some of these pieces are not available for your tank because of its class or nation, or the tier where it's in it just isn't good in.
In this part I'll go through which tiers benefit most from each equipment piece. However, I will exclude the Gun Rammer from each tier, as it's the one piece I expect you to put on any tank no matter what.
In this tier, you're often fighting inexperienced players who understand little about the game. The most efficient way of dominating this tier is with vision. However everyone is driving either light tanks or medium tanks, so you need to buff up your camo and view range to avoid close combat with multiple tanks.
Priorities: Coated Optics, Binocular Telescope, Gun Laying Drive
Now tank classes spread out a lot more. You'll be fighting more heavy tanks and medium tanks, and unless you're in tier 4 light tanks become significantly fewer in each match.
While view range games are still viable at this tier, some tanks become open-topped which buffs their view range significantly and others just get good base values for no real reason while others get terrible view range. Think of the T40 and KV-1, respectively.
Focus on maximizing your tank's performance, view range often comes second.
Priorities: Improved Ventilation, Gun Laying Drive, Coated Optics, Camo Net
Often known as the tier of the heavies, this tier is terrible for mediums and tank destroyers are generally weak. Most tanks get a significant view range buff compared to their tier 5 or 6 tanks ahead of their line, but often you can't play with view range unless you're a tank destroyer or bespectacled heavy.
Last to note, the Americans start to get Vertical Stabilizers at tier 6 in the case of the M4A3E8 Sherman, and tier 7 for the T29. Put this piece on these tanks!
Priorities: Improved Ventilation, Gun Laying Drive, Coated Optics
Finally we start heading into tank destroyer territory. At these tiers, you get punished very badly if you make a mistake. High-alpha heavies, tank destroyers, self-propelled guns, autoloaders, and mediums with lowerful damage per minute and penetration.
You'll probably want to focus on survival at this tier or learn the hard way that active play is not welcome in these tiers. Unless you have a platoon.
Priorities: Vertical Stabilizer, Coated Optics, Improved Ventilation
And this is where the metagame embodies itself in its final form.
You'll want to aim fast, reload fast, stay hidden, and run away fast in this tier. Staying alive and dealing more damage is the goal of this tier, and you should have your equipment mounted accordingly.
Priorities: Vertical Stabilizer, Improved Ventilation, Binocular Telescope
Lastly, for the hell of it, I'll list the priorities you should have on each specific tank class.
This is a general guide, and some tanks will stand out as a certain piece being an odd pick on them. Maybe your medium is really slow, your heavy is really fast, or your tank destroyer has a turret. But in most cases, the following picks are correct for the tank class as a whole.
Lights: Binocular Telescope, Gun Rammer, Vertical Stabilizer
Mediums: Coated Optics, Gun Rammer, Vertical Stabilizer
Heavies: Gun Laying Drive, Gun Rammer, Vertical Stabilizer
Tank Destroyers: Gun Laying Drive, Gun Rammer, Binocular Telescope
Self-Propelled Guns: Gun Laying Drive, Gun Rammer, Improved Ventilation or Camo Net