"Best" and "most significant" are not, of course, completely coincident. I think one can make a case for the Corsair (F4U-4) being the best fighter-bomber (I'm not going to try -- the entire concept of "best" is too subjective), but I think there are other aircraft which were more significant in the fighter-bomber role, possibly including the Hurricane, P-47, Fw190, Typhoon, and others.
Ahh, F4U fighter-bombers in Europe, what a great thought