The other day I was watching a Simpsons episode and I said to myself: "man, The Simpsons is like the most influential TV of my life". I said it without really thinking of it, and then I thought, "wait a second, let me actually think about it". And think that The Simpsons indeed are the piece of television that have shaped my life the most. I grew up with them (I think to really be impactful in your life said TV show or movie would have to be part of your life in your formative years).
I think a series has a higher probability of being impactful since they more chances (more episodes) to leave a mark one like a of movie.
So think about it, think of your everyday life, of the things you hold dear, of the things that you may quote constantly. What is the most influential TV show or movie of your life?