This was a hard list. Just looking at Wikipedia for ideas of universes to include, you would see tons of universes that are all worth at least a mention, and more still that would probably take weeks of research to judge fairly. Rather than attempt to do that (and most likely turn this into a top 20 instead of a top five) I decided to take the more well-known universes and judge them that way (so maybe this should say MY top 5 sci-fi universes, but oh well.) Take a look and see what I came up with!
5. Halo universe
One of my personal favorites, this pseudo-earth future has power armor, giant space ships, and intelligent AI! This place has it all!
4. Warhammer 40k universe
Take a normal sci-fi universe (Does that even exist?), add fantasy races like elves and orcs, and then crank the intensity dial up to 11. That's about what the 40k universe is like.
3. Doctor Who universe
Tardis, Sonic Screwdriver, and Daleks, what more could you possibly need? OK, maybe we could to without the Daleks, but with Doctor around I'm sure we could live with them, right?... Right?
2. Star Trek universe
These last two on the list place so high not because they are so much better than any of the other fantasy worlds on this list, but because they are some of the earliest examples of popular sci-fi culture. Star Trek takes number two probably because of an internal bias I have, but this could just as easily be number one.
1. Star Wars expanded universe
Star Wars has become one of the largest sci-fi franchises in history, and that's not just wishful thinking. Looking objectively at the franchise, its net worth has grown massively since Disney has gotten its hands on it, and those numbers show no sign of falling anytime soon. Oh, and I include the expanded universe in here, because even if Disney doesn't recognize the expanded universe, I still love the lore. This franchise sits deservingly (I feel) at number one.