Vice Admirals don't get a free ship. To get a better cruiser than the Assault Cruiser you need to either buy a Z-Store Ship like the Odyssey or Dreadnought Cruiser, or get one of the Fleet Cruisers from a Fleet with a sufficient shipyard. The Fleet Assault Cruiser needs a Tier 5 shipyard.

There are also Lockbox Ships that are pretty good, but they cost lots of credits. The Galor and D'Kora are both popular Cruisers. Or you could get lucky and win one by opening a lockbox, but know the odds are against you.