The Poseidon Class and the Vindication Class have good roles to be advanced UNSC ships, but then we would need something equivalent in the Covenant. (Don't say Covenant supercruiser, it's already in the game and is the Covenant equivalent of a Valiant Class Cruiser. Both focus on boosting Fleet Range or just having a long range in general.) Some good options would be
Reverence Class Cruiser
RCS Class Armored Cruiser
ORS Class Heavy Cruiser