Tetris was the one I played the most for single and multiplayer, just an excellent version. For stuff originating on GB, it's a tough call between Donkey Kong '94 and Link's Awakening. Bionic Commando's also up there.
That’s a tough question to answer but I’d probably have to go with Tetris or links awakening although I never played links awakening until I had it on my 3ds. But I used to play Tetris with my friends with the link cable all the time back in the day.