At first, my reaction was "Monty Python", no doubt. But then I started thinking, and now I can't decide. Both have great collections of movies, but I am going to pick MP for the Flying Circus tv show.
National Lampoon has dropped some real turds in recent years, but I'm guessing that's not the collection you're referring to.
National Lampoon only has two things going for it. 1) Animal House. 2) The Vacation Series. Maybe you include Loaded Weapon and/or Van Wilder but that's kind of pushing it. Everything else has pretty much been crap. While I love Animal House more than anything Monty Python, it can't lift up the Lampoon Collection as a whole above Monty Python.