I cut my teeth on the 1911, and personally, prefer the grip angle on the HK over the Glock. I can't naturally "point and shoot" a Glock as quickly. All the same, I own several of each. My G30 is still a favorite and is extremely accurate.
You know, although I generally really like H&K products, but I just have never warmed up to the USP model. I have handled them at many of the gun shows, but there is just some kind of body language between my hand and the gun that sends me the wrong signals. I can't put my finger on what it is, whether it is pointability, balance, bulk, whatever, I just have never had the desire to buy one at all.
And as for the Glocks, I had a model 17 and just didn't like it at all. I was glad to get rid of it when I finally traded it off at a gun show a while back.
So if I had a gun pointed to my head and forced to choose between one or the other, I would have to go with a USP in the hopes that it would eventually grow on me after I had it for a while. I bought the Glock thinking I would like it, and didn't, so I know there is no chance of it growing on me if I got another one.
That's funny! I, recently, had to make this decision for myself. I decided on Glock because of: Better (but, not great) factory service, the design allows me to do most of my own gunsmithing, and standard (full) capacity magazines are, both, more plentiful as well as easier to find. I, also, like the way my Glock Model 21's shoot; and, although price wasn't a criterion, Glock pistols cost significantly less than H&K!