Sonic 2 for me. It was the first game I played when I had Sega and it's still a nice game to play. The end credits were beautiful, the gameplay was awesome and it was nice beating Robotnik and all his odd cadgets. I don't know why I liked this Sonic game the best - perhaps it's so because it was the first Sonic game I've ever played. But, Sonic 2 is dear to my heart and one of the best platformers I've played in my life. Sonic & Knuckles would be my second favourite.