I mean pathfinder is sorta my current go to but you know one of my favorite groups I was in the dm used the hero system where he used the champions variable power pool for spells so that you can describe to him what you would like a spell to do and he would sorta run it through to see how much mana it would cost and if its doable and would suggest ways to save or such with it. It was a blast. sci fi is tough because I liked playing d20 star wars but also like star frontiers and like d20 babylon five. so the systems made and integrated with the ip were sorta nice. that being said I used to love star frontiers. for superhero I like champions. champions online is actually sorta cool as it uses the rules as a basis for the game which is why you can freeform characters.