Really tough one this. I suspect Schindler's List is the best film he has made; it is not the one I enjoyed the most, however.
I know he has wrote/produced loads of ace films like The Goonies, Poltergeist, Gremlins, Back To The Future etc... But for the poll I'll just do ones he has directed. Again, can't fit all of them in so if I've left your favourite out vote other.
On another note he is making a film of this book Robopocalypse: Amazon.co.uk: Daniel H. Wilson: Books anyone read it? Film due out 2013.