HK holds 50% more rounds, at the cost of grip size. HK can be carried cocked and locked, Sig cannot. Sigs can be bought certified pre-owned from the factory, USP cannot. Other than that, they both are accurate and reliable.
But then, the Smith 4566TSW is on par with the USP and P220 in this size, and the CZ 97B, and Ruger KP90 are excellent as well - all of which can be had NIB for $375-450.
As for me, I chose a 4566TSW, and an HK P9S-45 Target as my non-1911 45s.