I, for one, have to admit I have a preference for a big one, I think they look better, feel better in my hand or mouth and, by and large, are more satisfying if used correctly.
However, I must qualify this by adding that, for me, thickness is more important than length, the girth is what gives the pleasure.
Given the choice I would take a short thick one over a long thin one.
Now, having said all of the above, a big cock is a not essential, if I met a guy who I really cared about and he was small in the downstairs section, I would not walk away, it's not THAT important. And if it helps I can confirm that the biggest guy I've had was an awful lover and some of the nicest sex I've had was with a really small guy.
Confused? You will be! ;-)