Mallrats is quite easily the funniest- it goes Mallrats, then Clerks, then Jay and Silent Bob Strike Back (although that was a hilarious movie). Dogma and Chasing Amy were nowhere near as funny, but then again they weren't intended to be and more than make up for it in other areas. I personally think Chasing Amy was the best made movie and Mallrats was by far the funniest.
The Clerks cartoon was very funny as well, although I think they only made some 11 episodes. However, I do remember hearing Kevin Smith is making a Clerks animated movie, so that's a plus.