It's hard to decide. Dreamcast and X-Box had far too many few games that I actually wanted to play, though I still have my DC and couple of games for it. Just for design, Dreamcast is one sexy beast, and definately wins in the design department.
I'd REALLY consider voting SNES, not that I've ever had it (my friend actually has it, so I have played it), but they've made so many good games for it (like FF6).
Then again, I've had PS/PS2 for ten years now, so I guess I'm kinda biased, many fond memories of that machine. They've also made a couple of magnificent games to it (Resident Evil, FF Tactics and FF IX, Driver, Wipeout and Die Hard Trilogy for example), so I guess I'll vote PS1.
Funnily for the PS2 I've only found one game I truly love, that being Ring of Red (that game rocks

, anybody ever played it?).