Here's a quick assessment of how i view the ships.
Scouts - great at absorbing scout fire so your rippers don't get shot
Rippers - great for killing transports
Transports - great for holding troops, decent at destroying barges, can kill rippers
Barges - they steal stuff
Cordova - Expensive but very effective at killing barges
Cont - large flying target
Fort - Larger flying target
Dom - great at killing scouts, which we have allready established are fodder anyway
Personally, I used to rely on rippers, but this round has gotten freaky transport reliant, so it's almost impossible to have enough rippers to shred an opponents transports.
As it stands a good mix of Scouts, rippers and Transports are a good mix for defense, of course strongly backed by Troops.
Life is the teacher,
Pain is the lesson,
Scars are your diploma.