Mk23 is the correct answer here. 🙃
But if we must choose between the HK45 and USP, and both isn’t an option, then it most likely comes down to hand size. I love the feel of the HK45 in my hand, but I shoot the USP better. If you have smaller hands, the USP may be a bit uncomfortable to hold. As others have said, being able to hold or, better yet, shoot them would be ideal.
I actually prefer the HK45c over the HK45 or the USP, but whichever one you pick will get the job done.