I haven't played through all of them yet and if they weren't free I probably would have only got SMB and maaaaybe Mario and Yoshi. So far I think that Balloon Fight, Ice Climber and Wrecking Crew are all great and, despite knowing so much about it already, Zelda has blown me away. I think it's mostly because it's in such a raw state and it's soooo huge that it looks anything but effortless.
Still, my favourite game is still SMB 


I spent another entire Summer playing Zelda 2 and let me tell you, I was obsessed with Zelda back then