I tend to be a little bit of a Sony person, as a PS2 owner, but I'll try to offer a more or less balanced look here:
Games: If your choice is about current gaming, or about current online capabilities, then your only option is the Xbox 360. If those two really are your primary concerns (which they are for many people), go with the 360. Done.
Minor note with online play: If your friends all don't own the 360, the online play advantage might not exist for any system. This depends, of course, on your situation.
High def player: If your choice is, to a large degree, to buy an HD player in addition to a gaming console, it's the PS3, hands down. HD-DVD will be around for a while, but it's dying off, even now. IMHO, PS3, no contest.
As you're buying from Costco, repair isn't really an issue. Disc scratching is scary, but not quite epidemic level yet. Worth caution? Yes. Worth not buying a good system over? No.
Me personally, I know I'm going to have to buy a blu-ray player eventually, so I definitely will buy the PS3 at some point. I'll only buy the 360 if I decide I really need to play a game on the 360. Right now, sad to say, the only game that really excites me on 360 isn't Gears or Halo, but Dead Rising. Xbox has the advantage of some great exclusives, but they (mostly) don't interest me.
So my advice is--take a look at your situation, take a look at what exclusive games interest you, and make a decision from there. There's not going to be a "winner" per se in the console war, so the most hardcore of hardcore gamers are stuck with the worst possible option: buying all three. Just choose the one that best suits you, as we won't see a major industry leader this generation.