Numenera written by Monte Cook, its Earth but a stunning nine civilizations (only some were human) rose from the stone age to technological peak before collapsing again one after another. This results in so much unexplained tech it may as well be magic. Magic users are simply manipulating the nanobots in the air for example. Very fun setting with a great world map.

GURPS is what I've run before.

Always wanted to run Skyrealms of Jorune after playing the computer game, but it remains in the box.

I really want to do a game that's like a riff on Shadowrun. Near future transhumanism, magic, and the players go and blow up a board room full of oil executives or health insurance leadership or what have you.

I enjoy high fantasy with a touch of post apocalyptic sci-fi. I ran a Palladium Fantasy RPG campaign set in post apocalypse Robotech. Basically it was my version of Rifts, which is another setting I greatly enjoy.

But in the end I think I will almost always find Star Wars to be my favorite. I have made my own systems that are outside the Empire/Republic, my own crime rings. I have exclusively played the WEG d6 version, but am going to give the EDGE system a try after my D&D campaign is done.

I really keep trying to shoehorn sci fi into D&D 5e but it never really works, much to my annoyance. Particularly, trying to get people to learn additional systems is hard, so I keep trying and failing.