For simplicity, I've stuck with the VERY EXCITING early 80's concept of "bringing the arcade home." I've picked these all for the same, simple reasons:
a) They were almost better than the original arcade version i.e. slightly easier but still amazingly fun.
b) They ran the best, fastest and smoothest and took the best advantage of late 70's, early 80's Atari technology:
1) Defender: this game is amazing on an Atari. Fast, smooth, colorful, with great early arcade crunchy sound effects.
2) Donkey Kong: faster and slightly easier than the original game -- arguably better. Great fun and extremely addictive.
3) Galaxian: bright, colorful and packed with motion and smooth animation with nutty sound effects. Simple and replay-able over and over and over.
4) Pacman: Yes, it came out on the 2600 first, but the Atari Home Computer version was the best kept secret for a long time. Beautiful, bright and accurate with great joystick response, it starts getting very fast and very furious after about 20,000 points.
5) Pole Position: It didn't matter that you didn't have a steering wheel or foot pedal. Atari made the acceleration automatic, with you in control of the shifting, brakes and steering. Set it for 8 laps and screech around the curves, trying to not go up in a ball of flame and beat your own record times and number of cars passed.