I wonder if owners of either could chime in on their thoughts. From my understanding is that apart from ergonomics and actual aesthetic look they share the same reliability and accuracy.
I have owned both. I think that the hk45c grip is slightly slimmer, not much but enough that I liked the grip of the usp45c better. the HK45c has an o-ring on the barrel to help with accuracy and barrel lockup, plus it also has the match trigger internal parts, just not the match trigger with over travel screw.... when i had it and my usp 45 tactical the trigger weight and reset were almost identical to that of the hk45c. So overall i liked the hk45c trigger better than the uspc trigger. besides that the hk45c has a standard picatinny rail and a full hammer that is easier to access. Overall i like the hk45c more than the usp45c, except for the grip, and the price, but i got a hell of a deal on my hk45c, so it wasn't too bad for me....