Scorpion gunboat is the best in the game. It has 8 guns, while being quite fast (almost as fast as the light ones, IMG and Rogue, a lot faster than the 'sair one). I have tested it with some friends and it can really out turn slow GB's, while being able to shred fast GB's to pieces. Also, it's cross-section along the Y axis reveals its not such a big target as the Corsair one, and it's able to dodge fire more effectively when circling capital ships.
The best bomer... I am in a tie between the Catamaran and the Snubnose.
The Catamaran has supposedly a small size, the small bomber powerplant, and very limited armor. But what's the matter if they can't hit you, right?
The Snubnose... Interesting ship... Due to Rheinland factions having a bad name when dealing with indie military (I have no firsthand experience, just what i have seen while lurking) and due to the fact Rheinland is dead most of the time (traders usually and the occasional BH farming Wilde) it's a ship that has not been in the spotlight alot.
Well, the Snubnose is a very very good ship (if one of the best anti-cap bombers). It has a relatively small size almost comparable to the Catamarans, while having good armor, the large bomber powerplant and decent agility. And 5 guns. It's not on the slow side of things either, it's manouverability is decent. The only dealbreaker is the non-fitting hitbox. I extends infront of the cockpit alot.