Atari 2600, easy. We never really got new games as kids so we got a LOT of Jakk's Pacific Plug n' Plays. We got the Atari Flashback one Christmas and even in the mid 2000's I still found the 2600 library very fun. Some of my favorites are:
1.) Adventure
2.) River Raid
3.) Haunted House
4.) Secret Quest
5.) Pitfall!







