Both guns are great IMO.
I am shooting a Standard HK USP9 and 40 (conversion kit) for about five years now, and I have 20k+ rounds total through the gun. Reliability is 100%, I never had to replace, "tune" or "break-in" anything on the pistol. Same mags, same springs. Only the .40SW slide shows wear, but I shoot really hot stuff. When I last checked (somewhere after 15K rounds), accuracy was under 2 inch at 25 meters, offhand.
The USP is definitely NOT a racegun and never will be, but I think it's an excellent all around, low maintenance pistol, for the average IPSC shooter. I see only three weak points,
- trigger and trigger reset (could be fixed by Bruce),
- control lever/decocker (unintentional decocking could be fixed by switching off the decocker),
- weight (you gotta live with that, it's a polymer pistol)
The recoil is not as bad as some think... In fact, I (the poor level "B" guy ) wasn't impressed by the recoil management of the stock, untuned EDGE .40 against the USP40, using the same ammo. The magazine release is extremely fast, just like on the P7, but takes some to to get used to it.
Anyway, I think the P226 ST is a better choice if you only shoot Production.
For Standard AND Production I would pick the HK again from this two.