Well, Premiere Pro is probably used by more people around the world than Avid, FCP, Vegas, Edius, and Media 100 combined. However, the only place I've seen it used professionally (on a large scale) is a TV station in the Ukraine. I know lots of others use it for broadcast content, and it's perfectly capable to, but it's not generally looked at as a "professional" app (even though it is).
So, that leaves you with FCP or Avid (according to your list). Buy a Mac and install both. Avid can be installed on a Mac or PC, and you'll do best to learn both programs. Avid is still dominate in the broadcast and film arena, and FCP has a huge following in the indy market (and a huge amount of post shops that work on TV, Film, and commercial work).
If budget is a big deal, FCP is cheaper than Avid. Plus, Avid is supposed to be making a big announcement this month (by Friday), so hold off on buying Avid until they say what they have to say. They might be killing off Xpress Pro (pure speculation on my part), or they might be introducing new hardware (still speculation).
Either program will get the job done--contact a dealer near you for a demo of both to see which you like better. Or keep using Adobe. Their integration is the best I've seen, and that counts for a lot if you're a one-man-band who does graphics, editing, sound, etc...
Regardless, try out all the systems first to see which one you like better. And as far as future proofing--unless one of those companies announces they're going to shut down in the near future, they'll keep issuing updates and trying to improve their product. That'll protect your future a little bit.
there are no stupid questions, but this is a stupid question, unless you are building a rental facility (in which case, you were given the right answer - build both). It is YOU that have to make this decision - not us. You have to decide which software you like better - you are the editor, not us.
Some people like FCP, some people like AVID.