Just 5? I can't do multiple lists with 5 by platform?
OK, here goes:
1. Donkey Kong
2. Centipede
3. Asteroids
4. Captain America and the Avengers
5. Teenage Mutant Ninja Turtles: The Hyperstone Heist
Those are 5 of my go-tos. I first played Donkey Kong on the Atari 7800, but I have a Famicom copy that I play on an American NES clone using a pin adapter. For Centipede and Asteroids, it's got to be the arcade or Atari versions. The last two are beat 'em ups that I love for the Sega Genesis. Though, Captain America and the Avengers came out in the arcades. But, I've always played it on the Genesis.
Though, if you want me to, I can do top 5 lists by platform for Atari, NES, Sega Genesis and Super Nintendo. I play classic games all the time, I love them so much better than modern games. (current console gen, I still like stuff from the last few generations)