I have a 9mm USPc, and I've shot my buddy's .40 USPc. Both are excellent guns. Accurate and reliable. My biggest gripe is that hi-caps for the 9mm are extremely rare, and I've never seen .40 hi-caps.
Also, while I've had only limited experience with the .357 Sig, I can tell you that ammo will be more expensive than 9mm or .40, and if you reload you will have trouble finding brass (for every couple hundred rounds of 9mm or .40, I find about 10 rounds of .357 Sig brass).