My opinion follows similarly to the lines of Phantom Warrior.
Glock 19 vs USPc, my vote would be the Glock.
Both weapons are spectacular handguns, The glock and USP are both Reliable. Both are "relatively" lightweight. But the USP doesn't really doesn't fall into the compact category. Its on the big size in terms of being compact.
What I do like about the Glock is the easy manual of arms. Just pull the trigger and it shoots. Its also very easy to field strip as well as detail strip. At 21 oz empty, this gun disappears and you wont even know you're carrying it. The Glock is much thinner and smaller than the USP so it'll be easier to conceal.
The USP has pretty good ergonomics, the option of using DA/SA or condition one (cocked & locked). Only thing is, the frontstrap and backstrap checkering really does hurt. After firing the USP .45, I round my hands to be sore from the checkering. I even had indents in my fingers from the checkering. That sole reason turns me away from the gun. Otherwise I would truly consider one, very much.
Hold the Glock, see how it points. Then hold the USP, which feels more natural to you? For most people, including myself the Glock points naturally high. I have to readjust my grip to get it to point straight.
The USP's grip might fill your hand better, since it has the thicker grip of the two.
Only way to see which one feels better to you is to rent them at the range.
Good luck