When I was younger it was Nightmare on Elm Street. Since I aged it turned to Friday the 13th. Jason is such a badass and I love watching him walk straight for his victim and give um a slash. Sort of like Cloud's Limit Breaker.
The Friday the 13th series gets my vote. I just love the cheese. There is no cooler killer than Jason, no one even comes close. I have seen every single movie in the series, and while there were a few even I couldn't really enjoy, I have liked 90% of the movies this cheesy series has put out thus far. I also thought the remake was far better than Rob Zombie's Halloween remake. We'll have to see how good the Nightmare On Elm Street remake is before I crown F13 the king. Ha.
But if this has been a multiple choice poll, Scream would've also got my vote. It brought the slasher genre back from the dead and had so many quotable lines that people continued to say for years after the movies had come out. I am eager to see if the fourth installment ever sees the light of day.