Star Trek: The Next Generation. Being born in the early '70s, I grew up watching the original Trek series on Sunday morning re-runs, but when TNG came out when I was a teenager, it felt more my speed. A wider range of characters, the stories were more involved, etc. The original series was a great starting point but I feel TNG really expanded and added more depth to the Star Trek universe, and it's that series that most of the subsequent ST series appear to most try and emulate. Also, my favorite Star Trek movie is from the TNG cast, Star Trek: First Contact. It's almost like a zombie movie in outer space, and being a lifelong horror fan, that really appealed to me.
All that said, I also saw the original Star Wars on opening weekend, at age 6 or so, and it blew me the f*ck away. Imagine being a child seeing that movie for the first time, on a giant movie screen, at a time when there had literally never been another movie like it. It was one of the most powerful film-going experiences of my life, just mind-blowing. And while I liked The Empire Strikes Back, after that I felt the movies got worse and worse as the series went on. I haven't even bothered with the last two or three.