Well Star Wars goes on top for sure, it's a truly unique sci-fi universe bordering on fantasy sometimes.
Battlestar and Stargate take a shared second place, I love both equally but for different reasons. Battlestar is an almost (well no, it just is) a mystical storyline embedded in an incredibly awesome setting with fantastic characters and character development. And Stargate, well it's just purely awesome in it's cult-ness. The main characters are awesome, and the universe is suprisingly rich, even though it's plagued by human/human-like species, but at least they have a good excuse for it, unlike Star Trek, wich is why Star Trek has to take a 3th spot sadly. But then again, I still love Star Trek a lot.
All in all, all sci-fi universes rank extremely close to eachother. They all have their good and bad points, and I almost love them equally. Why should you have to pick? Just go for all of them!
Ok given, Star Wars ranks pretty distinctly on top, mostly because it has the good points of all other universes rolled into one, plus it's so extremely rich and detailed, you could get lost for weeks in all the fluff. And I love fluff.