X-post from reddit:
I wrote up some initial thoughts regarding propulsion a while ago, and I'll quote it here below:
Propulsion type and build strategy are tightly coupled
Propulsion type primarily affects speed, support, and integrity
A mismatch between propulsion type and build strategy leads to underperformance
Choice of propulsion type can transform over a run
Flight
Fastest speed, lowest support, lowest integrity, hopping over robots ability
Key stats define it as extreme propulsion characterised by avoidance of confrontation
Low integrity exposes it to massive attrition if damage is not avoided or mitigated well enough
High speed amplifies energy costs and heat generation
Arrays trade some speed for support and reduction in energy/heat effects
High speed and the flight bonus leads to high evasion, which can be effective damage avoidance if maximised
Low support benefits more from low mass items such as processors, hackware, melee weapons, light power sources, sensor/scanner utilities, and power amplifiers
Low support means minimal inventory space
Hover
Fast speed, moderate support, moderate integrity
Key stats define it as flexible propulsion suiting a hybrid approach of not avoiding all confrontation
Excellent balance between speed and support suits endgame play
Significantly worse than flight for confrontation avoidance, which it must make up for with robustness and some combat ability
Relatively rare and therefore vulnerable to attrition
Fast speed must be taken advantage of
Wheels
Moderate speed, moderate-high support, moderate integrity, low penalty
Key stats define it as suitable for maintaining moderate speeds while significantly overweight
Low penalty is best taken advantage of with a minimum of propulsion slots (excluding propulsion armour)
Low end wheels common on main floors but high end wheels are significantly rarer
Exposed to traps while overweight
Legs
Slow speed, high support, high integrity, kicking ability (+20% chance per active slot)
Key stats define it as flexible propulsion for combat focused play
Most common type found from hostile robots and high integrity makes it resistant to attrition
Treads
Slowest speed, highest support, highest integrity, no self-damage when ramming ability, crushing ability (chance varies), reduced recoil (-1% recoil per active slot)
Key stats define it as extreme propulsion for combat focused play
Vulnerable to traps
High likelihood of triggering traps and slow speed reduces the importance of staying under the support limit
Exposed to extermination clock due to slow speed
Reduced ability to avoid combat and therefore alert gain and item attrition
Recoil reduction benefits kinetic builds the most
Propulsion doubles as effective armour
High end treads somewhat rare but last a long time
Often occupy two slots per item (especially at endgame), preferring an even number of propulsion slots
To continue...
My favourite propulsion is flight. This should come as no surprise to anyone. It's sleek and elegant. My favourite items in the game are lightweight and go perfectly well with flight. Hacking is extremely powerful and pairs perfectly with flight. Having a significantly faster movespeed than everyone else opens up a lot of options. The big downside is how fragile you are.
You can play flight in a variety of ways. Any number of propulsion slots is perfectly viable. With just two, you can run an ultra light hacking build. It's over the top but it works. With a dozen prop slots, you'll be using a whole lot of propulsion armour (inactive treads and legs which serve as massless armour) and you'll have heaps of spare flight units already equipped and ready to be switched on whenever you need them.
The sweet spot is definitely 4-8 prop slots though. Even numbers are better because of flight arrays, which are extremely strong and pragmatic. Impulse thruster arrays support 27 mass for two slots spent, which is 13.5 support per slot, but also have the cost of a typical one slot flight unit. They can also be fabricated in pairs. They're certainly not the best flight units but they are so useful in transitioning to a high-end flight build or just completing a w0. The best flight units for mass support are 16 support per slot (imp. q-thruster I think?).
A lot of the time I play with 6 prop slots because it's 'just right'. You reach something like 20 speed with endgame flight units that way with about 80 support, which is enough for 2-3 lrg storage.
One big vulnerability of flight is stasis traps. If you're running 'tight', with no excess mass support, you're going to get stuck in one for ages. Some methods to counteract this:
* Ensure that you never get hit by stasis traps. This means having operator allies, hacking machines and robots, and exploring through rooms as much as possible instead of using hallways.
* Have excess propulsion slots with flight units ready to be switched on to 'burst' through the stasis.
* Have treads as propulsion armour and switch them on for the one or two turns it takes to break free.
* Have stasis canceller utilities at the ready. I don't like this because it's so niche and consumes a slot, even if it's an inventory slot.
Flight is very tough early in the game. I still do switch to flight very often in Materials, but it's not exactly optimal to do so. For years, the preferred strategy has been to play combat early on and accrue a number of items to be used in a switch to flight around the end of Materials or the start of Factory. This is still the way to go. Materials is very confined and difficult to avoid enemies in, and early flight units are so fragile that they'll be blown off with a single bad hit.