I don't like the Imperial designs very much.
The Courrier looks like a Formula 1 "car" (I don't think they are cars, more like little kiddy carts).
The Clipper looks like a fat plane, with overly complicated wings, and no tail.
The uggliest would be the Clipper.
I like when ships look like the serve a real-life purpose, when you see the scraps and bruises on the metal. Apart from the Imperial ships, all of the other ships have this kind of look, to an extent.
My favorite designer is Core Dynamics. I like the angles and the aggressive look of those ships, as well as the cockpits (those textures…

)
All of the above is my humble opinion, your mileage may vary.