I have a few that are right up there too close to call an outright winner.
Planes, Trains and Automobiles. It is one of the funniest films ever made and Steve Martin at his very best.
Scrooged, a different take on the Dickens classic, sorry but A Christmas Carol has been made so many damn times, and all of them done the traditional way it gets stale. Scrooged however went its own way incorporating many great dark comedic moments.
Its a wonderful life, what can anyone say other than it is a true classic.