My thoughts on:
Drake class - looks like it used to be some mega ship, then split in two, welded carrier part in the middle and done. Front part itself looks even nice but then ends like a fish's cut head. Engines looks OK, compact. Just it doesn't "play" as a whole.
Fortune class - bulky, sturdy and tough like a pack of nails. This comes to mind first when I look at this one. Engines are cool looking while head part reminds me FatBoy - experimental tier mobile artilery unit from Supreme Commander. Generally Fortune looks like FatBoy that went to space.
Nautilus class - nice looking bulb head that fits nicely to the carrier part behind. Rear underside part is... interesting. Lots of parts and construction that look they are hanging. Engine part is ok-ish, due to down slope being the main motiff it feels like there's something missing on top. Front mountet "bridge" section is also nice.
Victory class - c'mon, Hammerhead corvette from SW all the way. The most balanced build, save for the massive head part which makes it massively top heavy. Engines are nice looking, underside is not overbuilt. But that head...
If I was to pick one it would be ... Nautilus.
Despite Fortune has better looking engines and Victory being more overall balanced in shape (minus head), Nautilus is a frame to go for me. Bit lacking in the rear part (flat end with downward slope) and whole bunch of stuff underneath but generally, for me, it's the best looking one.