I am being completely sincere when I say that McClellan had one personal aptitude to being the Press Secretary: a dry, boring style that never made a good soundbite/clip for the MSM. Ari Fleisher and Tony Snow had real presence and clear intelligence which made them more apt to be used in soundbites/clips with the downside being that any "mistake" they made would come across as more theatrical than McClellan.
In the end of course McClellan, like any Press Secretary, is going to be utilized in soundbites/clips no matter what. I just believe the only effective style he had was to sound like a funeral director and thus lull some of the press into a gentle nap.