Sonic Advance 2

It depends on what you'd like to achieve; if you prefer to clear the levels as quick as possible then pick sonic as he's the fastest character. however if you want to collect the chaos emeralds then knuckles will prove more useful with it's climbing ability (which is not limited like tails/cream flying)

In my personal opinion, it has to be Cream (although I prefer to use Sonic). She has a nice speed, great boost abilities off of ramps, she can fly and her chao attack can bring down every boss in the game with ease.

Sonic has quick speed, great jump height and awesome boost abilities. Although he lacks the ability to climb walls or fly, Sonic really doesn't need those extras.

Tails doesn't jump as well, his speed isn't as great, and his boost abilities are poor- especially off of ramps. He does have the neat ability to fly which can help skip corners and gain higher ground easier than other characters.

Knuckles for me is the weakest character. His jump is average as is his speed and for me he has the worst boost abilities on the game. His abilities to climb certainly make it easier to find those elusive rings though.

Amy has very nice speed and a great hammer boost skill. Her jump isn't the best nor is her close range attacks, but over all, Amy is a decent character.

Depends on what you want. Sonic is the fastest character, Tails and Cream are for flying, Knuckles can climb and glide, and lastly Amy just has a hammer (though is a little fast).