There are two other teams on Sonic Heroes besides Sonic and Dark: Team Rose and Team Chaotix. Team Rose consists of Amy Rose, Big the Cat, and Cream (along with her chao friend, Cheese). Team Chaotix consists of 3 lame characters that were in "Knuckle's Chaotix," which I have never played, and haven't heard anything good about.
I'll probably rent the game, and play it through with Team Dark (Because Rouge is rocks my socks, and you can't go wrong with Shadow). If it's any good, I'll buy it used. After all, Sonic was my first video game love... namely, Sonic The Hedgehog 2 for the Genesis.
Tails is the best.