This list is purely by aesthetic / model, though in-game other factors are considered before buying a ship.
Hard to pick one, so I will just put top 3:
Fighter: Plover, Claymore, Defender
Bomber: Pytho, Blacktip, Roc
Freighter: Kestrel, Clydesdale, Rhino
Transport: Kaiser, Mammoth, Bison/Stegodon
Gunboat: Condor, Defiant, Imperator (really wish the 2 heavies are at the front 2 slots instead)
Frigate: Peregrine, Raba, Salvager
Cruiser: Storta, Donau, Resheph
Battlecruiser: Interdictor, Komainu, Tirpitz
Battleship: Valor, Overlord, Ranseur