Pretty difficult because I have a lot of experience with all of these guns. I especially like the glock 22 and the USP (although my USP is a .45, and it isn't the tactical model). In my opinion, the USP is a higher quality gun, and it,s very easy to shoot well. The trigger is awesome, and I like the DA/SA options. The USP also seems to manage recoil better as well, but with all that said, I can buy two glocks for the cost of a USP.
If money isn't an issue, I would say go with te USP. Otherwise, go with the G22 and never look back.