"Actually, I'd recommend getting Ruby or Sapphire over any upcoming variant. If you have one of those, you'll only need to find someone with the other to catch them all. If you get "Emerald" or whatever comes out in the future, you'll have to trade with both Ruby and Sapphire owners."
That's not how it worked with R/B/Y (I'm not exactly sure about G/S/C, but I thought it was the same). Yellow had all of the "rare" Pokemon that were missing from either Red or Blue, but was missing it's own Pokemon that were previously thought to be common, because they had been in both Red and Blue.
So all you needed was access to two colors in the series, any two colors, and you had a chance to get all of the Pokemon.
If you're buying only one version, then I don't think it really matters much which one you get. If you're buying two, because you have friends willing to play Pokemon, but not willing to buy Pokemon, then I think it's a good idea to get one of the first two, and then hold out for the third one, because you tend to get a bit more "variety" in the gameplay and storyline that way.
"I have never played a single Pokemon handheld game (though I did rent the N64 ones and didn't like them, but those don't count). I also did not like traditional RPGs up until about 2 or 3 years ago, but now I love them. Would you recommend that a non-Pokemon fan pick up one of these? and which one would you recommend getting (though it probably doesn't matter too much)?"
Red and Blue are the originals. They started (so they predate and weren't "affected" by) "The Pokemon Craze". They're simply GameBoy RPGs (from the original black and green "GameBoy" days) that can be judged like any other RPGs. IMO, they're a bit dry, but extremely unique, which makes it easy to see how they kicked off their own "craze".
Yellow has more of an anime feel. Which either helps offset the dryness of the first two, or makes you run away screaming, and cursing the name of Pikachu. Considering that you were able to rent the N64 games, I'd guess you can handle it.
Gold and Silver have a very cool 7-day-a-week 24-hour clock thing. The early bird gets the worm, so if you want to catch one you're going to have to actually drag yourself out of bed at 6:00 AM on a Sunday morning and get out there to hunt one. And then there's the coolness factor of the "shiny" Pokemon that you have a 1-in-100,000 chance of finding.
Crystal is just G/S with the chance of playing as a girl (or so I've heard).