The Sphinx's look interesting but I have no experience with them.
If you don't already have a 226, I would tell you to go that route. Make sure to add the SRT(if the one you get doesn't come with it) and the Gray Guns P-SPIT trigger. It really sets the 226 over the top. I have - and really, really like - the MK25. It is my favorite gun overall. Get a bunch of the MecGar 18rd flush fit mags to go with it. The 18 and 20rd MecGars is all I run in my 226. The OEM mags sit in a box in the closet unless I'm going out to burn through a ton of ammo, then I'll take them to the range so reloads are less frequent.
The only initial complaint with the MK25 was holster compatibility because of the 1913 rail vs the standard Sig rail. No worries though, I had a beautiful kydex pancake holster made for it and picked up the the Comp-Tac Infidel (which I use most often).
The USP is also a very nice gun though - especially if you go with the Match or Match-LEM hybrid trigger systems.