I have (among others) a USPc 9mm and a P7M13. Both are excellent guns in their own right.
The P7, however, is heavy. It also heats up so bad after about 50 rounds that you can't shoot it any more (not a problem for concealed carry unless you carry more than 50 rounds on you). It is beautiful to shoot and very accurate. There's also a certain mystique to the P7.
The USPc is also an excellent gun. My biggest complaint is that 13 round clips are very hard to come by, although they do exist. The USP, however, will hold more rounds than a P7M8 (the same as the P7M13), and is substantially lighter. It also doesn't have the heat problem that the P7 has.
If I had to choose a gun whose primary purpose would be concealed carry, of the two I'd go with the USPc. However, I would also check out the Glock 19/23 and the Walther P99 before I made that choice.