@Sonicman
Playing with Sonic & Tails, or just Sonic, or just Tails, will give you the same story for the most part, but you will need to be playing as Sonic (with or without Tails) to get to the real final battle...
In Sonic 2, Tails following you seems to make the special stages more complicated. In these games, it does not seem to be that way.
Also, when playing as Tails, he can fly in this one, where in 2 he can not.
I know I'm going all over the place but also, when playing as Knuckles through the Sonic 3 levels, he will take some different paths then Sonic and Tails.

