I have had the opportunity to shoot all the USP's and they are great guns. I have also shot the HK45 and if 45. is the cal you are looking for I would highly recommend the HK45 over the USP45. Both are great but the HK45 was pretty much designed to be an improvement on the USP and I must say IMO it is.
I recently was at my local shop looking for a 9mm and ended up putting a deposit on an HK P30L. It was really between that and the USP9 and the P30L was significantly more comfortable. The HK45 is very well balanced and comfortable as well.
NRA Life Member