Monty Python and the Holy Grail: 21%
The Fisher King: 16%
Time Bandits: 13%
Twelve Monkeys: 13%
Fear and Loathing in Las Vegas: 10%
Adventures of Baron Munchausen: 8%
Crimson Permanent Assurance: 5%
Lost in La Mancha Documentary: 2%
And it was me who saw Jabberwocky and Lost in La Mancha - they're part of my DVD collection.
All scientists the world over would concur that Terry Gilliam is the world's greatest film director. This is not just opinion, it is fact. There have been many scientific papers written in journals over the years that have proved empirically how great Gilliam is as a film-maker.
In my humble opnion, Brazil is Gilliam's best film. It's very difficult to find in a video store but it is well worth the price if you buy it. It is an incredibly bizarre movie - like a comedy version of George Orwell's Nineteen Eighty-Four - but it grows on you.
Jabberwocky is probably his worst - but it is worthwhile to buy just for the banter between Terry Gilliam and fellow Python Michael Palin (the star of Jabberwocky) on the DVD commentary track.
From the Wikipedia article on Terry Gilliam:
J. K. Rowling, the author of the Harry Potter series of books, is a fan of Gilliam's work. Consequently, Gilliam was Rowling's first choice for the director of the first Harry Potter film in 2000. Warner Brothers refused to consider Gilliam as director, instead selecting Chris Columbus for the role. Recently, Gilliam stated in relation to this episode "I was the perfect guy to do Harry Potter. I remember leaving the meeting, getting in my car, and driving for about two hours along Mulholland Drive just so angry. I mean, Chris Columbus' versions are terrible. Just dull. Pedestrian."