3 Desolators, 1 Evacuator with Drain Planet up, 2 Carriers, 1 Marauder and 1 Desolator, and planets will go BOOM insanly fast!
More seriously (well I'm serious in fact with that combo but it is not often I can get it up, 'cause I do mostly pvp), my favorite Vasari's cap ship is the Evacuator, due to his drain planet ability and earlier the Nanite Disassembling ability. Both are pretty nice, add this the colonize ability and you have a decent ship to ruin your oponnent's day.
As for a second prefered cap ship, comes the carrier and the desolator, altough the desolator need to be at least lvl 4-5 to be really interessting in planet ... pacification, that's why I usually do a duo or a trio of them, if I can (and if things are going really well, i purchase them their lvls, letting them be lvl4, wich at that point I send them heavily escorted (thanks to RA) to a pirate base to improve their lvl before sending them wrecking havok to the foe's planetary asset.
I cant give advice for others races since I dont play TEC, and very rarely Advents.