I've had both. For carry, I think the HK45C wins out slightly due to the geometry of the slide. Aside from that, there isn't much difference. I still have the HK45C, I no longer have the USP45C.
"Throughout history, it has been the inaction of those who could have acted; the indifference of those who should have known better; the silence of the voice of justice when it mattered most; that has made it possible for evil to triumph."
-Haile Selassie I