I have both.
My USP9 is a tactical model so you get a better trigger than a standard USP.

For the questions you asked they are a complete wash.

The only places I find they are not a wash is weight (metal vs. plastic of course) and the Sig is far more comfortable to shoot.

The simple answer is own both.

I answered USP for lower recoil in part because of the "designed for .40" part, but the .45 USP is the softest, most pleasant polymer .45 I've ever shot (including the HK45). I'd trust either with my life and others, but SIG wins hands down on trigger pull. Accuracy is a wash, but not even the match trigger in the higher end USPs even get close.

At the end of the day I don't think you'd lose either way but I'd prefer the 226 for my one gun. Nothing wrong with the HK and I prefer the mag release but the 226 may be the closest to perfect gun. Atleast for me. It feels great in the hand, points naturally, its very accurate and reliable.