I vote for wheels, too!
I ride a Logitech MomoRacing - good wheel for small money, but meanwhile I would rather tend to a Logitech DrivingForceGT, for having a bigger steering angle. Quality between those two is (in my opinion) the same - good wheel and horrible pedal. Had a Logitech ForceEX before, which was really imprecise with weak FFB and broke after only 3 weeks. If you can afford the price, G25/27 or Fanatec are the wheels to look at (clutch pedal and way better pedals overall).
Edit @jb:
Don't think that keyboard has that much advantage... Surely, the PC helps you breaking, steering and all - but for much less control and sensitivity. I think it needs a very skilled keyboarder with hillarious fast fingers to beat a skilled wheeler.... or am I wrong?