I've no experience with the PX4, but the TM usp is fantastic. It's now my go-to sidearm. It gets nothing but propane thrown through it and it just works fantastically. The main thing for me besides the aesthetics, is the mag release. I find it much more natural to have it where it is on the USP across the base of the trigger guard than a button. I can drop the mag with my ring finger or thumb comfortably. Had a Glock initially (cant remember which gen, but the one with the larger mag release button) and I found I occasionally caught it when gripping the gun quickly and dropping the mag.
If you're just plinking and not worrying about panic reloads while getting shot at, just pick the one you like the best.