Most: PS3 with 69 games (including one not logged in this site's database but I'm too lazy to enter it myself... it's Demon's Souls but the Korean version)
Because there are a lot of great games from that generation, including many exclusives I love (BlazBlue and Disgaea come to mind immediately). And so many of them are cheap right now, so I'm playing catch-up in getting all of the ones I really want.
Least: Nintendo 64 with 5 games.
Because it's the newest console in my collection, and while I have a list of 15 more games I need to collect sometime, I'm not in any hurry to get them. I'd like to get games for all my consoles, not just one.
And I know better, know that I should distinguish between GB, GBC, and GBA, but I tend to think about all of those consoles as a collective since I only own a GBA SP. So for the sake of being 100% accurate, the least is actually GB, since the only game I own is Super Mario Land.
(Actually the least games I own for any console is 0 since I don't have any Atari games, or any XboxOne games, or and Genesis games...)