So we played BFG last night and I think everyone enjoyed themselves. For those that have not built their Imperial or Chaos cruisers, one way to decide which cruiser to build would be to consider which battleship you might want in the future. It will be highly unlikely to field more than one battleship in a game. Thus if you want a carrier as a battleship, build no more than one cruiser as a carrier. If you want a gunship as your battleship, then at least one, if not two, of the cruisers should be carriers.
Chaos have 3 battleships available: the Despoiler (carrier), the Desolator (gunship), and the Planet Killer (gunship)
Imperial Navy has 5 battleships available: the Emperor (carrier), the Retribution (gunship), the Apocalypse (gunship), the Oberon (gunship-carrier mix), and allied Space Marine Battlebarge (gunship-carrier mix).
Necron, Tau, Corsair Eldar all only have one battleship choice.