Simple answer is , if you are locked to AT&T or Verizon you have the option to try one and buy the other,
If interested in either and it were me making the choice, I'd buy the iPhone as the first option, try it for 30 days or more, then sell it if I didn't like it and buy the next phone. But I would do it before the iPhone5 came out, since all the other iPhone's prices will drop like rocks and whatever you paid for it, you won't get your money out of it, no matter how nice it is, 30+ days later.