Just going to throw my thoughts in because I was doing something like this anyways:
First thing, Cost and OP and to a small extent availability should be factored in (how easy can I mass this, and does that change anything about it basically).
Capitals:
Astral- I'd give it an A- but whatever. That special ability is so insanely good.
Atlas/other cargo/fuel ships- It bothers me that trading in this game isn't really a playstyle (even illegal smuggling) because you can pretty much mark every single Cargo/fuel ship as a passive upgrade and then MAYBE care about how fast they go.
Legion- I'd probably move it to an A. It's always good to have since fighter/bomber support will always cover weaknesses and it'll still delete the hell out of ships in AI hands.
Onslaught- I'd drop it to a B/B+. Solid, reliable, good, but nothing amazing. I'd take the legion over it every time.
Cruisers:
Dominator- Solid C in my eyes, but maybe i'm building them wrong. For the OP/Cost I almost always want to bring something else, even if it's just more frigates/destroyers.
Gryphon- AN odd one, but an easy B in my eyes. In the players hands it's just broken to the point of being silly and by far the best alpha strike hull I've found (fly in, delete a few things, retreat, fly something else). In AI hands it's not stellar but still one of the best hulls for turning overloads into kills if you load it up with harpoon pods.
Mora- B+, the fact that it punches WAY above its weight and is very easy to obtain and deploy. A single mora early game is a great flagship or support, and you can actually get a fleet of these quick and seriously wreck shop as long as you find half decent bombers.
Starliner- no really...whats the point of this?
Venture- C. It is without a doubt the worst combat cruiser in the game, but what it really is is the poor mans heavy destroyer. The default loadout makes a great escort ship as it'll pop shields and punish with it's missiles and do pretty great PD thanks to the drones and flak. I'm generally happy to pick one up in the early game.
Destroyers:
Buffalo MKII (all versions): I hear you can do things with them but in a game where the AI sees you with no shields and just nukes you with hapoons this has certainly felt like a pretty solid F everytime i've ever bothered. Maybe an LRM platform, but then I could just not do that.
Condor: D+. The + for being the "i need a carrier yesterday" option for difficult starts. I don't think you ever wind up keeping it.
Drover: B-. Might have to do with my AI struggles. They're a little too good at getting close for my tastes in AI hands and lack the punch to make that safe. That said it's actually a very fun combat carrier.
Enforcer: C? I look at the loadout and keep thinking it should be better, but I've almost never been impressed with them.
Gemini- C- for being a way to turn your cargo into something you aren't terrified to deploy and basically a better condor.
Hammerhead- B. I'll always take a hammerhead as long as I can get the tech to kit it out half decent, which is pretty easy given how flexible it is.
Harbringer- I find it very hard to judge phase ships because due to their cost, rarity, OP, and drawbacks i'm almost always too worried to even let the AI touch them. In human hands like most phase ships its a crazy good alpha strike ship.
Medusa- B-. If only because it's harder to find/equip and a little more fragile than a hammerhead.
Mule- D+ I want combat trader to be a playstyle so bad, but it just feels like pulling teeth. Maybe i'm building it wrong, but so far I've never been impressed. The + is because sometimes early game you just want a freighter than can fight, but unlike the gemini I wind up a lot more worried my cargo capacity might explode.
Sunder- B. This and the hammerhead are the Ryu and Ken of the game to me. A large energy + its ship system on a destroyer has some very efficient burst options for the OP, and it's super easy to make an AI variant that'll handle itself and still clean up.
Frigates:
Afflictor: no idea. I've almost never gotten one.
Brawler (normal) - B. Damper field is just so wonderful.
Brawler (TT) - C. Maybe i've been doing it wrong, but I find these things to be made of paper and rarely if ever able to justify their slots due to flux issues.
Centurion- C-, at least that's what it's felt like the few times i've tried to use it. Seems like an escort ship, but man color me unimpressed. Damper field is still great, but unlike the brawler it's just not a threat.
Cerberus- D. If star sector were a Saturday morning cartoon the villains henchmen would fly these.
Houd- D. Or these...for variety.
Hyperion- Can't really class it. From what i've seen it's no where near worth it in the hands of the AI and fails critically in every possible way, even with builds that don't really take advantage of it's nature. In human hands it's a very expensive way to get to delete a few ships before leaving. I suspect it's really more of a B since it's just so damn impractical when you can accomplish most of the same effect that it has with other, less interesting, ships.
Lasher- B. The hammerhead of the frigate world.
Monitor- D. Might just be me again but this is like a Brawler/Mora, but with shields....oh and unlike those ships you never actually care if it's still alive. The mora is a real threat and the brawler is a big enough thorn that you're often stuck trying to avoid it since killing it is a pain. I mostly just ignore monitors and feel that it's gone the same way when i've used them.
Mudskipper MK.II- D+. ONLY because if you can get a mass of them things start to get silly. Probably an F and i'm just too excited about dumb gimmicks. Especially when you consider that almost every large ballistic weapon EXCEPT the gauss is even more terrible on it. The gauss at least lets you mass them on escort on a carrier so they can provide fire support from relative saftey. Everything else gets them in firing range which means they're a great way to get rid of all those extra large ballistic weapons you don't want taking up space. I also never found any medium that was all that impressive.
Omen- A The Emitter is crazy powerful, extra so on a maneuverable frigate hull. The only reason it's not a + is because it shares weaknesses similar to phase ships in that i get a little worried giving it to the AI. Still fairs way better than them though and can just murder its way through a ton of OP.
Scarab- C. I think I used it once and while fun I was heavily unimpressed. From a strategy standpoint it just didn't feel very good. From a "fun to fly" standpoint it's an A.
Shade- another phase ship, another hard to say.
Tempest- A+/S-. I will always take a tempest. Always. They do anything and everything and they do it all well, and a huge part of that is because in human hands they're crazy and AI hands it's hard to screw up having an Ion pulse drone.
Vigilance- C+. I don't actually hate them but I often wish I had something else.
Wayfarer- D. I feel like if this game supported the millenium falcon playstyle, this would be that ship. It doesn't, so meh.
Wolf- B-. Flexible, powerful, reliable. My only issue being they're harder to find and outfit than a lasher, and with a bad layout they're awful in AI hands.