I gotta say Dreamcast, if it had the chance it deserved. So if i compare the time it lived (just over 3 years i believe) to the time from the start of the other consoles till they where the age of the Dreamcast, then definitely the Dreamcast. In the short time it lived there where a lot of amazingly good titles on it.
Otherwise i go for the Xbox. I dunno, they're all awesome. The PS2 has plenty of great games too, but so does the GC, especially in multiplayer games.