D20 Sci Fi games?
I own Dragonstar, Prime Directive, Star Wars, and a few more. Of them all, I like the Traveller D20 game the best, but I could see a good arguments being made for using Mutants & Masterminds or Spycraft 2.0.
I've been playing Traveller since it first appeared, so that is part of my bias.
Spycraft has some nicely done variant rules, and by its nature, it handles high-tech weapons pretty well.
Mutants & Masterminds has the advantage of flexibility. By their nature, you won't find a more flexible game type than a Supers RPG (their source material ranges from pure fantasy characters to ultra-hard sci-fi). Any concept you want to model, you'll be able to.