Carriers on the whole are pretty weak right now and need to be beefed up to be honest.
Ugh, so tired of hearing this. Sova, yes, I agree it's not that great. Skirantra has an area of effect healing ability; this is nothing to scoff at and probably one of the game's most powerful abilities. Oh yes, it doesn't help much against focus fire, but if those are the kinds of units the enemy is using why did you pick this capital ship? Against illuminators or flak (or a starbase, though going toe-to-toe with one of those is normally foolish), it's a lifesaver! The Halcyon is an absolute monster with telekinetic push and energy amplification aura; its other abilities suck, but those two are seriously insane.
Egg is pretty good, although the colonize ability isn't as good as the Progenitors. Egg could be a bit less vulnerable. Perhaps give it the firepower of the Akkan and you'll have one hell of a ship.
Pretty good? You're talking about one of the strongest capital ships in the game. Yes, the Progenitor's colonize is better, but that's also one of the strongest capital ships in the game (imo Progen is the strongest). This capital ship already does absolutely insane damage in the form of nanos. If it wasn't fragile with low damage, it'd be a nearly unstoppable killing machine. It's constantly spitting out death sentences to enemy units in the form of nanos, and even enemy capital ships must run in fear if it turns to face them, because their health will disappear in a heartbeat.
Antorak is useful in some situations, useless in others. When you compare the overall usefulness against the Dunov or Rapture, it is clearly inferior.
Antorak really can't be compared to any other capital ship in the game. Really the Sova is probably the only equivalent to the Antorak.
A Vulkoras is a heavily armored siege platform ... unfortunately, in this role, I would have to argue that the Marza is better (and is a better warship as well)
Simply comparing raze planet with siege platforms and you are correct. However, the Vulk's passive ability makes it the most powerful siege capital ship in the game overall. It's more specialized than the Marza, but it is certainly the better of the two in terms of this one specific role.
Talk to most people and you'll generally find agreement that Progen, Egg, and Marza are the three best capital ships in the game (imo in that order). Other powerful capital ships are Radiance, Halcyon, Kol, and Akkan. Underappreciated gems include the Rapture, Dunov, and Skirantra. Less powerful (but still useful) capital ships include the Vulkoras, Revelation, and Kortul. The situational (that is to say, usually very weak) capital ships are Antorak and Sova.