Pad users have an advantage for sure, always will. I know I have personally lost a competition (for a trip to the Japan GP
, was left with just a small HDTV ) to a pad user and simply to the speed he could turn the wheels (after the comp I did testing with the pad, made significant gains in tight turns against my wheel ghost).
Pad users can with practice (and in game smoothing) become very, very smooth which is the only said advantage of a wheel. Also wheel users control two inputs with their feet. Fingers are far, far better suited to this and are designed for precision, your feet are simply not.
In short:
Pad Pros:
minimum lock to lock time the game can produce
precision throttle
precision braking
Wheel Pros:
in some games a wheel can be smoother if the game does not support pad input properly
its more fun?...