I can't miss this thread, so I'll add my two cents. Which look just about the same as everyone else's two cents.
Star Fox 1 was groundbreaking for its time, but it's aged terribly. Don't recommend.
Star Fox 2 was even more groundbreaking, well, had it been released back then, but has aged even worse. Don't recommend.
Star Fox 64 is fantastic, a truly great game. It expands on the ideas of the SNES originals, but this time with actual frames, and passable graphics. Simple story but charming characters really sell it. Great gameplay. Short playthrough, but loads of replayability. It's by far the best in the series.
Star Fox Adventures, uhh... it plays more like a Zelda game, but with a key difference: it sucks. (It also wasn't originally meant to be a Star Fox game, which, beyond making it a different experience from the others, also created an issue with the IP by adding a lot of stuff that really doesn't fit with the series.)
Star Fox Assault is mixed. There are a couple of really fun levels in it, a lot of bad levels, and atrociously bad controls. They had many great ideas with this one, but the execution was rarely up to par.
Star Fox Command is a thing that exists, I guess? Everything it "added" to the series sounds like terrible fanfic, so, nah.
Star Fox Zero is also mixed. There are a couple of really fun levels in it, a lot of mediocre levels, and a couple of bad levels. And also atrociously bad controls, although for me they became playable once it "clicked" (not fun, just playable). That never really happened with Assault's controls. It has its moments, but isn't very recommendable.
tl;dr Star Fox 64, yeah, go for it. Either the N64 or 3DS version will do - yes, the 3DS audio has been entirely revamped, with most of the music sounding less moody than the original, although I'd say some tracks were improved upon (they totally butchered the main menu theme, though). And the voice acting is less memorable, but still pretty solid.