Best in Nintendo: Gamecube (platinum version) / Worst: NES (I love it, but man is it ugly) Virtual Boy is sexy, you guys are nuts
Best in Sega: Sega CDX / Worst: Dreamcast
Best in Sony: PSOne / Worst: Playstation
Other beauties: NEO GEO AES, SNES, N64, Virtual Boy, 360 Slim, Saturn
Ugg-o's - Xbox, 3DO FZ-1, Most Playstation Consoles, 360, Most Sega Consoles,
I think the ugliest system for me has to be the original Playstation though. Truely vomit inducing
Sexiest for me is likely the Platinum Gamecube (even sexier with a GB Player).