What's the best Carrier? Depends on the situation and what build you want.
Vo'Quv wins in tanking abilities simply because its so large and has so much hull (and with 2 Lt. Cmdr slots). Fantastic tanker if used properly, stick a CPB3 on there and the fighters will just obliterate opponents .
Kar'fi in regards to more Sciency debuffing abilities. I use Tykens Rift 3 on it and, together with the Energy Siphon fighter pods, completly drain opponents. Combine this with Chroniton torpedoes and maybe a mine launcher as well as a tractor beam, then your laughing. Plus, I find that using evasive maneuvers to bring my cannons to bear makes me just laugh even further because you have enough DPS to kill them.
I'd say both are brilliant. Yes, Vo'Quv has been nerfed like nothing since launch but is still one of the best tankers out there. Kar'fi simply isn't the best in my view because its a +1 or it may have better turn rate, but it does have strong shields and it great at shield tanking.
Orion Marauder? Tried it, better than Star Cruiser but would rather stick to my Bortas