My vote for the ugliest is the A2090 card. I ought to scan mine in. It had various components haphazardly placed, clearly without much forethought. It was also ugly to use.
The most good-looking piece of Amiga hardware are the Amiga computers themselves. In particular, the Amiga 1000, the A500, the A2000, and the Amiga 3000. My favourite is the Amiga 2000, because it allows you to hide an awful lot of ugliness inside. Can't say I'm too keen on how the other Amigas (A600/1200/4000/4000T) turned out.