i have a usp (in .40) and have fired the p226. i find the usp a bit akward as the grips seem too small for the slide and my hands, but i added a rubber grip to fix that (but i still can't hit anything with it) and it also tends to jam, but i think thats a mag related issue, which is a shame cuz they are really expensive mags compared to glocks and sigs. other wise very nice, has the external safety and de-cocker, the trigger is a little loose when cocked but easy to control.
the p226 was a very nice nice gun to say the least, and as someone else mentioned arts are cheaper and easier to find than HK parts. accurate and reliable i dont think you can go wrong either way. If you want to use jack bauer as a reference he used both the HK and Sig.
I say Sig. it has better ergo's for me and i like the way it shoots. if you have the opportunity to try both obviously do it. But i liked the sig better than the usp which is quickly becoming a safe queen..
This my opinion only from my experiences, it is up to you to make your own!