As a kid, some of my fondest memories were of watching Star Trek: The Next Generation with my dad. But I remember after ST:TNG ended, I started getting really interested in Star Wars, buying dozens of the novels and obsessing over the movies. I eventually stopped right around the time they started the New Jedi Order. I think Episode I pretty much was the beginning of the end for me and Star Wars.
What defines both Star Wars and Star Trek for me are their second-released parts. To me, Episode V and The Next Generation just transcend everything else in either of those universes. That's when both "jumped the shark", so to speak. Looking back at my experiences with both of these rich sci-fi universes, I'd have to say that Star Trek edges out Star Wars, mainly because of Capt. Picard, Data, and the rest of TNG.
Really though, I think George Lucas ruined Star Wars for me. Both by having I-III be so cringe-inducing at times, as well as unnecessarily fucking around with the original trilogy.
Gene Roddenberry on the other hand is dead, so you can't blame everything afterward on him like you can with George Lucas.
I could go on and on and would like to do so, but it's late and I really have to go to sleep soon, so I'll just say this:
Star Wars taught me how to dream, but Star Trek taught me how to live.
More later, maybe about my Star Wars novel collection, idolizing George Lucas for a short time, how my personal beliefs were shaped by The Next Generation, or owning the entire TNG series on DVD.