Best TTRPG system for swords-and-rayguns classic sci fi?

[robkelk]

(GURPS Space combined with Lowtech/Dungeon Fantasy are not disqualified if you really think that's the best. I'm just looking for opinions.)

In that case, chapter 7 of GURPS Mars might have you covered.

The problem with having been in this hobby for what is now approaching fifty years is that I've seen hundreds of game systems come and go.  I know I've seen something along the lines of what you're looking for, but damn me if I can remember any specifics.

At least we can safely eliminate The Spawn of Fashan from consideration.  <grin>

I think that goes without saying...

Space 1899 isn't bad, really. It depends on which rule system you use.

Heroes of Mars uses the FUDGE system. It's pretty closely tied to Barsoom as a setting. On the other hand, it's free. YMMV depending on what you think of FUDGE.

Barsoom again: This one's wargaming, not RPG. It's free because the copyright wasn't renewed. It might be of interest for the historical value, seeing it's 50 years old. Warriors of Mars: The Warfare of Barsoom in Miniature (1974), by Gary Gygax and Brian Blume. (Download the PDF, not the EPUB.)