If you're looking for shooters, it's pretty simple: get a 360.
I would agree that if price is a concern, that may be a deciding factor for you right there. I don't want to spend over $400, so I'd hold off on both PS3 and Elite. However, I'm not so desperate for the lackluster early lineups and can wait for both to drop to that.
If you really only want one platform and can live without Nintendo's games, the Wii needs to be eliminated first off. As much as people may pray otherwise, the biggest non-Nintendo franchises will remain on 360/PS3 (spinoffs notwithstanding), with the PS3 having the edge with the Japanese developers and the 360 havinig the edge with the PC developers. System sales won't change any of that, unless Nintendo can manage to outsell the other two combined, and even then I wouldn't bet on it.
I personally am growing more and more impressed with Microsoft's internal stable of talent. They've been aggressively acquiring with no apparent end in sight. But then I do ask whether I'd be willing to sacrifice things like Square, Koei, and Konami for something like Banjo or Fable.