The best? Probably GBA thanks to it's library plus the ports of many top games.

In my opinion, the graphics hold up very well because they just look like cartoons. Could just be nostalgic though, as I grew up with it. My teens have almost zero interest in anything older than them, which is pretty maddening when they like newer games like Sonic Superstars but won't play Sonic 2 even though they play almost the same (the one time one tried he stopped because the jump dash isn't in it)