TV definately for the reason that Dream Weaver mentioned. A film throws every plot twist and character at you at once. There can be no cliff hangers or true plot twists than affect the story in the long term. For example, imagine LOST as a film? Nooooo. TV shows forever!
Hmmm this is difficult as TV gets boring... things repeat and it just gets really annoying although saying that if there's a good series of something on then I would probs prefer the TV but otherwise I love movies