Sonic. The original and still the best!
I do enjoy the faster-paced action you get with Sonic, but that doesn't neccesarily mean the speed alone is what cuts it (Sonic Advance 2, I'm looking at you); probably, in some senses, the difficulty of the character, especially in the older games. His lack of secondary ability makes it hard, or impossible, to avoid most challenges, like with Tails or Knuckles. Remember those spinning tube-cages in Flying Battery Zone?
Also, I like the character for who he is. Not angsty like Shadow, and really not childish as Tails, and just plain not-stupid like a certain red echidna. Just carefree. :3