What is winning in retribution

G4 Legions, Ravyn with Hyperion (Defenders/Legions/FoW all have shouts for effectiveness, my inclination is for Defenders), Issyria Shadows...

Depends what the local meta is like...

there's a lot of dependency on what you're going to see locally here, but for my part:

4shade is currently ret's best caster. he offers relevant ARM and DEF debuffs into most matchups, can cloud wall a bit, ghostly and DR are relevant in all of the themes he fits in, and his feat is strong in most matchups. with revive and DR he's really the only caster in ret that can give ret a passing chance at not just losing to attrition. he's strongest with legions of dawn, but there's relevant targets for dauntless resolve in the other themes he fits in. northkin trolls and some khador can give you problems due to cold immunity, but overall 4shade LoD is probably the strongest thing ret can field in a general sense right now. helynna in LoD is also very strong into a lot of shooting, but not quite 4shade effective.

everything else after that has holes. issyria/ossyan shadows, rahn FoW mittens spam or vyros2 FoW griffon spam, ossyan/ravyn DoI are likely the strongest, but all of them run into a similar problem in that ret just loses to attrition really fast. shadows and DoI will melt against moderate amounts of AOE, ret jacks are generally squishier than their counterparts in other factions, and rahn mitten spam is a meme list that is really fun but not overly effective in my experience. they all have matchups where they excel and matchups where they fall flat. most people at higher levels of competition tend to lean on issyria shadows because it's a strong anti-recursion drop that also deals with incorporeal and a few other things fairly well.

as for "for fun" lists, I've been enjoying playing thyron in FoW. the general idea is to surround him with jacks, get storm rager on him, and move him across the table to go do work himself in a butcher-esque idea. there's also playing elara2 with a lot of things, as ghostly+boundless charge feat turn gives you a delivery alpha that can shock some people, but if you don't basically win on feat turn she will probably lose to attrition because she has no defensive buffs and ret is so dependent on defensive buffs from their casters to simply live long enough to be relevant. kaelyssa is really fun to play into warmachine matchups, but she drops off hard into hordes.

I don't think that's really true. Plenty of caster/theme combos can function perfectly well from an attrition standpoint, depending on the match-up.

I think the difference is that Ret are a finesse faction, filled with relatively fragile high-value pieces - if you don't keep them safe and get value from them, you likely will end up losing the attrition.