Dahlsim pwns!
His zoning ability makes him the best character in the game.
His teleport is useless on the ground... but jump and immediately teleport behind them and you can combo into a fierce aerial punch, (short range) medium kick, yoga flame.
You can easily keep your distance with yoga flame and the long punches and kicks...
Another trick I found is to jump into a shotokan player or guile who is playing turtle game, then as they do shoryuken/flash kick, teleport backwards and aerial fierce punch.
Anyway... here's how you use him...
YouTube - Dhalsim vs. Ken part 1 Japanese Street Fighter 4 tournament
YouTube - Dhalsim vs. Ken part 2 Japanese Street Fighter 4 tournament