Marshall is consistently the funniest one on the show. Then when he goes on missions he is HILARIOUS. I mean, can you name a more comic episode than when he and Syd went to London? He freaked out on the plane, spoke Ewok, peed himself (just a little), got kissed by Syd, and rescued them both on that parachute ("My name is Marshall J. Flinkman and I am here to rescue you.") And, "If it's not Baroque, don't fix it."
I see Weiss as more wry and sarcastic than actually funny.