Sonic, obviously the fastest of the crew, has a double jump move able to clear certain areas.
His counterpart, Super Sonic, is literally unbeatable. You have to pretty damn shitty to lose with him.
Tails is alright, and he has his flight move for limited amounts of time.
Knuckles, almost as fast as sonic, can clear entire areas with his glide move that other characters can't.
Robotnik can shoot people.
Metal Sonic is basicly a faster sonic with the ability to glide on water for a limited time.
Metal Knuckles is the same way.
Egg Robo is just like Robotnik, but faster.
The weird Tails doll, was prime example of the level of detail they
DID try to put into the game...he's got a zipper and visible stitching.
Tails doll is faster then tails, but he is also much more creepy.