Sonic 2 is the best sonic game because it pretty much made sonic what he is today. I have played it on the genisis, emulated on android and on the xbox 360. The first game only had one level where you could go fast... green hill zone and sonic actual didn't really go that fast in 2 most of the level are focased on speed and you can do the spindash in sonic 2 witch is staple to sonic now.
I Know!! I love Sonic 2 too! One of the best if not the best of the series!
I do think that Sonic 3 & Knuckles and Mania are better, but Sonic 2 is in my top 5