If handhelds are concerned then I'd say the mighty Neogeo pocket; when SNK was not yet in Aruze's hands.
For worst I'll still go CD-i or 3D0 (they're damn near the same tbh). The 32X has Knuckles Chaotix, the best at the time home version of Space Harrier, and Star Wars Arcade.
I dunno, 3DO actually had a couple decent games. There's not really anything on the CDi that could qualify as even decent.
It's hard to choose just one, but I'd say the Dreamcast, Genesis, N64, and Gamecube all have a pretty good ratio of good to bad games; though they all have a decent amount of crap games. I'd add the Saturn as well, but I've only played a fraction of the games that were released for the system, so I can't really make a general comment on it.
I'll say the Sega Saturn in some ways is very similar to the Nintendo 64 in terms of the ratio of it's games to some degree.
The Saturn had a bigger library, though. Like I said, there are lots of games I haven't played. It definitely has some great games.
Wii U but only if a few more 3rd parties completely give up on it before the number of bad movie games and shovelware exceeds the number of ones found on Gamecube and GBA.