Dood. That's easy! Die Hard. Tho if I have to choose my favourite holiday episode of a TV series, Bones "The Man In The Fallout Shelter" pretty much edges out the competition thanks almost entirely to wet mostly nekkid Hodgins, tho the Remington Steele Christmas bottle show, and the Cupid ep where Trevor and Claire gets stuck on Jury Duty are also topping some lists.
ETA: Also, I should mention that prior to seeing Die Hard, my answer was always The Lion In Winter because it is the BEST dysfunctional family Christmas movie ever in the history of ever.