I have two of the P229R's, and they are my favorite pistol. They are a fantastic product that I would recommend to any shooter at any stage of their shooting career. I used to have a USP in 9mm. I wanted to love it, but after a year I traded it for a P2000 9mm... which I like much better.... Why? The grip. The USP grip blows. I'm 6'3", 250lbs. I think I have relatively "normal" size hands. I found the USP grip hard to really gain optimal control of the gun for fast shooting. The gun is pretty accurate, but I always felt like I was "re-negotiating" my grip with it constantly... and accuracy suffered. And I'm not just talking bulls-eye. I mean all aspects of accuracy.
The SIG on the other hand.... for me, at this point, it feels like I'm wearing my favorite pair of shoes or something like that. It inspires a ton of confidence. I feel like (and other people see) a better shooter when I shoot the 229.
The way pistols are designed.... there is always a trade-off between accuracy and reliability (including reliability without cleaning, torture-test mud/sand/water reliability). I think HK intentionally designed the USP with a little more focus on the reliability side than the designers of the SIG did. Both are very, very reliable... and both are accurate, but I think the SIGs are more accurate... the lock-up seems tighter, etc. That is just my view.
Here's a picture of the two together (and get the SIG, you'll be happier with it):