Sonic 3&K is better.....
Also, Generations is REALLY good. You should try it out, it's a great game.
Yes, you're right, 3&K was really good, but I liked the multiplayer mode better in 2. (and the minigame to collect the emeralds was more fun in Sonic 2, I hated the game where you had to collect this stupid blue spheres.)
Why would you recommend it? Is it like the old games? (Sorry, haven't heard that much about Generations)