Tier list of every single highest tier part in the game. I've played this game with each and every single part for quite a bit, but do not take it too seriously, this is mostly based on my opinion and on what I've seen people using.
The Tiers of parts from best to worst are:
S+ Tier - The highest tier, the best parts in the game that are available, what is mainly and most commonly used by the most builds and what is used by the meta builds.
S Tier - The second highest tier, can also be considered as the most viable parts.
A Tier - Third tier of parts, the viable parts that can do really well but isn't really the best.
B Tier - Fairly viable parts that can do well in some situations but are outclassed by others in most situations.
C Tier - Not very good parts, but they still can work fine depending on a situation.
D Tier - The least useful parts, barely used and having the most amount of disadvantages compared to the other parts in the game.
The Weapon Tier List
I will only be covering the highest tier counterparts which is T4/T5. There will be some exceptions like T3 Seekers, since it's very different from it's T4/T5 counterparts.
T4 Laser (S Tier) - Lasers are an amazing weapon for all situations, having good or even amazing damage at any range, requires you some aiming to do but it is a very good weapon overall. Compared to the T5 laser, you can place multiple of those on your bot rather than just one, two or maybe three. Due to how small they are compared to it's massive T5 counterpart, you can fit them on small builds.
T5 Laser (S+ Tier) - The T5 weapons are massive, having a huge amount of health, CPU and hitbox compared to their T4 or lower counterparts, even a single weapon can take quite a beating. Being the highest tier weapon, it deals the best damage.
T4/T5 Plasma (S Tier) - Very good rapid fire grenade launcher type of weapon against ground bots. It's best used on air bots. Deals huge burst damage, even better when paired up with an energy module. Easily the best hit-and-run weapon.
T5 Rail (S Tier) - It's a sniper. Best at long-range, having precise huge damage shots capable of disarming any T5 weapon in ~2 hits. It's projectiles are capable of slight penetration due to having 3 projectiles in one shot, which can ignore and plow through some damage redirection techniques.
T4 Nano (S+ Tier) - The only healing weapon in the game, it's ridiculously good due to its burst heal being able to save teammates in a pinch and keep them healthy. It's costly in terms of energy, but the heal is still really good even when you run out of energy.
T4 Tesla (A Tier) - A melee weapon, only really good on very speedy bots that can cross the map in seconds. Can easily vaporize any bots as long as you stick onto them with the teslas, doesn't consume too much energy either.
T4/T5 Flak (S Tier) - Really good anti-air weapon, denies any air bot going out in the open and forces them to stay on/near the ground to ponentially be hit by Plasma or Mortar. With max damage stacks, it can shred any air bot in seconds.
T4/T5 Seeker (B Tier) - Lock-on missiles, doesn't do huge damage and consumes quite a bit of energy, but it does it's job fine, be it as an anti-air weapon for air bots or something else. Can potentially scare away players into their cover just simply by pointing at them. The missiles can be easily avoided though by either going fast on the ground below them due to their not-so-much-fast turn speed, making them explode into the ground behind your bot or just simply getting far away so missiles dissapear.
T3 Seeker (D Tier) - An entirely different weapon from it's T4 and T5 counterpart. It's a homing peashooter launcher. Deals very little damage and consumes tons of energy. Other than making finishing off bots easier, it's not worth having at all.
T5 Ion (A Tier) - Close range shotgun type of weapon. Deals really good damage and doesn't consume too much energy, but requires quite a bit of aiming to do to hit all the pellets on the bot. Pairs up really well with speedy builds as well, yes, with planes too.
T5 Chain (S+ Tier) - Chaingun, shreds stuff up close and surprizingly good at medium-long ranges, very energy efficient and requires quite less aiming than the lasers, you only need to track the bots with it.
T5 Mortar (S Tier) - An artillery-grenade launcher type of weapon, dealing huge damage, having an amazing splash radius, covering almost the entire control point in Battle Arena. It does consume quite a bit of energy, so it's nice to have an energy module on your bot. Requires you to learn it's projectile arc, but once you get used to it, you can go ham.
The Movement Part Tier List
For this one I won't be covering their highest tier, rather will cover how good each tier of that part is.
T0-T1 Wheels (B Tier) - Small wheels are easy to hide behind some blocks, therefore easy to protect. Since they are also small, you can place quite a bit of them on your bot. Wheels aren't very good of a movement part due to how fast they and how most of the maps are bit claustrophobic. You can only move while on the ground, in 6 different directions.
T2-T4 Wheels (C Tier) - These medium-big wheels only have a single connection point, making them quite a fragile target if not having any damage redirection applied to that connection point. They are also harder to hide since their hitbox is pretty big. They are fairly decently tanky, but you can place less of them than their smaller counterparts.
T5 Wheels (B Tier) - These wheels being big and tanky also having multiple connection points (six connection points) compared to it's lower tier counterparts.
T1-T5 Thrusters (S+ Tier) - Helps you add an extra movement speed to your robots to the direction thrusters are pointing, 'nuff said. Speed of the bot can make a difference between anything, like stealing the far point, getting to your teammates in time to heal them with Nanos, etc. The smaller thrusters are also used to make a variety of drone builds, which are still pretty viable to this day.
T0-T4 Hovers (S Tier) - One of the best ground movement parts, easy to fit inside any bot, easy to protect, really good movement, great speed, probably also best backup movement part you can have. You can strafe and move in 8 different directions and due to its hovering ability, you can make your bot either rise above the ground or fall, making it 26 different directions. Though it's not as good as the rotors, which can move absolutely anywhere, be it ground or air in same amounts of directions.
T5 Hovers (C Tier) - While the hovers are good, the T5 counterpart isn't that much good, even though it has 5 connection points it has a massive hitbox which makes it really hard to protect, it requires too much CPU and while it does have a decent chunk of health, the health to CPU ratio is still low and it just doesn't really make it worth using.
T2-T5 Wings/Rudders (S Tier) - Most commonly these are used to make light plane bots, which are pretty good nowadays due to their speed and maneuverability. While the wings or rudders are a bit fragile, you can place quite a bit of them due to their fairly low CPU cost, plus the lower tier ones are smaller and can be fit any protected pretty easily, while the higher tier versions have more connection points, meaning many ways to keep the bot intact by rodforcing or strutforcing the parts.
T3-T4 Insect Legs (C Tier) - Doesn't do it's "sticking to the walls and ceilings" purpose very well, they are too big, mediocre speed, quite unstable sometimes, cost lots of CPU and have only 1 connection point.
T1-T5 Tank Tracks (D Tier) - Pretty much a way slower, but way tankier version of wheels. They have the highest HP to CPU ratio out of all the movement parts, having from 3 to 9 connection points depending on tier, but has a very slow speed and acceleration. The smaller tracks can be hidden behind blocks or protected with electoplates, while the biggest ones would probably be exposed, but due to their tankiness it's not much of a problem. What makes it so weak is that the tankiness wouldn't matter much, you would still end up getting destroyed relatively easily due to your very slow speed and acceleration and due to the fact you are just a brick that can't really do much when disarmed.
T2 Skis (C Tier) - Allows you to make very fast ground sled builds, which again has the same problem that the wheels have. They have the highest base speed in the game, which is pretty amazing, but they are pretty low CPU and don't have much health to CPU ratio, having only a single connection point, making them a bit fragile. They also require thrusters or propellers to work for each direction, therefore spending more CPU on movement, on top of that the bot must be quite light, meaning having less total health to CPU ratio of the bot. On the good side, they are relatively easy to protect, since you can only place them underneath the bot.
T2-T4 Rotors (S+ Tier) - One of the best movement parts in the game. Very easy to control and pretty maneuverable, being able to strafe and change height. Even though they have a fairly low HP to CPU ratio, they are pretty easy to protect by keeping them on the back, having everything like electroplates and blocks on the front and having camera + tilt enabled, making you always facing the enemy, plus having backup hovers inside a copter bot or mech/sprinter legs to retreat and heal in case someone goes behind and shuts your rotors down.
T0-T5 Mech Legs (S Tier) - Another very good movement part, having decent speed, maneuverability due to being able to strafe, jump and being able to climb some quite steep cliffs, a great HP to CPU ratio and ranging from 5 to a whole 45 connection points. The lower tier ones are fairly small and relatively mediocre in mass, making them a really good pair with rotors, while the higher tier ones have loads of health and connection points, but quite massive.
T3-T4 Sprinter Legs (A Tier) - Quite very similar to mech legs, having less HP but more speedier and more maneuverable, being able to do a long jump when reaching max speeds. With enough thrusters and/or propellers and having a light enough bot, the jump can be as long as almost the entire half of the map.
T3-T4 Propellers (S+ Tier) - They pretty much have the same function as thrusters, they give less extra speed but they give extra speed in both their front and their opposite direction, they can also act as a protective shield due to their pretty big hitbox, 3 to 5 connection points and a decent amount of HP and CPU.
The Other Blocks Tier List
Here I'll be covering some basic building blocks, modules and other kinds of blocks.
Medium, Heavy and Compact Cubes, Rods and Struts (S+ Tier) - Pretty much your basic building blocks and parts. You can connect the blocks inside the rods for some extra reinforcement or use struts as shields due to their high HP to CPU ratio.
Light Cubes (A Tier) - Light cubes are still fairly decent to use if you dont want to make your bot too heavy, be it in some places or just overall. They have a really low HP to CPU ratio, so don't spam them around too much unless you want a really fragile bot.
Electroplates (A-S+ Tier) - Covers and protects certain parts of the bot, having only 1 connection point till T5, where the biggest plates get ~6 connection points. The bigger the plates, the more coverage they provide and the more HP they have.
T3 Blink Module (B Tier) - A module that allows you to quickly teleport and cross a short distance. Good for things like escaping away to safety and such, but it doesn't have a very low cooldown so it isn't really fairly useful.
T3 Disc Shield Module (S Tier) - Creates a shield in front of you to block enemy fire. Has a decent amount of cooldown. Very good for protecting yourself or your teammates.
T3 Ghost Module (B Tier) - Cloaks your bot making it invisible, consuming energy for 10 seconds. It's a pretty decent module to flank enemies or for escaping away to safety, but it costs high amounts of CPU.
T3 Weapon Energy Module (S+ Tier) - Restores a certain amount of energy on use, has a pretty short cooldown, making it extremely useful for doing things like healing teammates when running out of energy or not having enough energy to finish off the enemy, etc.
T3 EMP Module (S Tier) - Summons an orbital beam that stuns, disables enemy bots and depletes their energy on contact for a short period of time. Doesn't cost much CPU, very useful module both for offensive and defensive purposes, like forcing enemies away from control points in Battle Arena.
T3 Windowmaker Module (B Tier) - Shows enemy locations to you and your teammates for a short period of time. Has the lowest CPU cost of all the modules and is quite underappreciated for what it can do.