I am a star wars man. The original Trilogy anyway. My favourite is The Empire Strike Back
Very hard to argue with a franchise that has millions of followers, conventions, guys doing the Boston Marathon in stormtrooper outfits. They have consistantly sold merchandise for the past 34 years. When I was a kid every boy had 20+ action figures. There are plenty of software titles out there too.
I thought George lost the plot a bit with the prequel Trilogy but they did bring a new generation of young fans in. Who else wants to see Ja-Ja fed to the Sarlacc? Where his ears will be digested over a period of 10,000 years? Perhaps we could throw whingy whiney Anakin in with him.
The next best Sci fi would have to be Star Trek which also has a massive following. Unfortunately I have never really got it.