I love Cardassian designs- there's sort of an art deco feel to their buildings and decor. Not too keen about the Cardassian fashion sense, though.
Glad I'm not the only one who thought "Deco" upon seeing Cardassian architecture! That was my first reaction, perhaps since Deco happens to be my favorite real-world architectural style. I think why I like Cardassian architecture is a lot like why I think things like this are gorgeous:
http://farm3.static.flickr.com/2274/1604541332_a1b8c01aa4.jpg
As for Cardassian fashion, I don't see what people find so objectionable to it (unless you're counting that unfortunate design from "The Wounded," which I suspect even the Cardassians themselves didn't like
)...I think it fits them very nicely. Garak in particular had a few that were quite flattering. Plus it looks like it would keep you warm in environments where the public areas are probably kept at bone-chilling temperatures because SOMEBODY keeps complaining that they're hot no matter what you do...
The other real favorite, architecture- and clothing-wise, has got to be Vulcans. There's something so regal about those robes in their more recent appearances, and I also love their writing system as well as the architecture we saw in Enterprise.
I think I'm a sucker for austere, desert architecture.
Anyway, I also have to give a special shout-out to the most recent Romulan uniforms. Those look pretty nice, and they also win in the starship department.
Bajor's pretty nice, too, although I tend to find other environments more attractive (especially deserts and rocky, dangerous-looking beaches).
