For instance, I just went on Amazon and found a used CIB copy of Sonic 3 for $5.59. It's one of the most common Genesis games around.
You can buy Sonic 3 and Sonic and Knuckles, and upon booting up Sonic and Knuckles, in the options it will allow you to play Sonic 3 and Knuckles. The best is the original Genesis, if possible, but if not, 360/X1. Frequently Asked Questions Whats the best console to play sonic 3?
