Jeff makes me laugh all the time with his quick little jabs. Vinny doesn't really make me laugh. Probably because I laugh at assholeish things and Jeff is an asshole. Vinny's too nice.
I don't remember what video it was in, but I remember one where vinny randomly just said "cunt". He always sounds so nice so even doing something that simple made me lose it.
Vinny's (generally) upbeat attitude is always welcome, and he's very funny, but Jeff tends to make me laugh more than anyone else there. Jeff's sense of comedic timing is really sharp and I love how casually dark he can be about his own lifestyle at times. His asides about his asshole of a roommate last week were outstanding.
Yeah, Vinny is my favorite but Jeff is right behind him. They make a great combo.