The worst.

[Montezuma/Kukulcan]

Worst Light Fighter: Caracal (it has roughly the same turning as the Eagle IIRC)
Worst Heavy Fighter: Paladin (just... bad)
Worst Very Heavy fighter: Nomad Assassin (hilarious hitbox)
Worst Freighter: Rhino
Worst Transport: Vache (it has few weapons, not much armour and turns like a Battleship)
Worst Gunboat: Bretonian Gunboat (huge and slow)
Worst Cruiser: Corvo (weak and pointless >.>)
Worst Battlecruiser: Either the LABC or the Argus (they are both absolutely terrible when compared to the Bullhead and Geb)
Worst Battleship: Either the Liberty Carrier or the Sarissa (both are epicly massive, and have far less armour than other ships of their size, and they are both greatly outclassed by their main opponants)

---