5. Sonic 3 & Knuckles - Pretty much the best 16-bit Platformer ever made.
4. Sonic Advance 3 - A cool blend of newer ideas, well done team gameplay, and classic platforming.
3. Sonic Adventure - The first true 3D Sonic platformer, with some of the best music ever, and great gameplay.
2. Sonic Generations - Made up for every game that sucked in the 2000s. Like Unleashed without the terrible werehog stages, and crappy physics glitches. Also, 2D stages. And was fast. Just really, really fast.
1. Sonic Adventure 2 - Somehow, even with it's flaws, whenever I think of Sonic, this is the one that always comes to mind. Plus, even if it was easy, that final boss fight is one of the most epic final confrontations in gaming history.