Great idea coming to a computer-centric forum asking about a Glock.
You now have one, maybe two, responses from people who have actually fired both the H&K USP and Glock to be able to make an informed comment, with the rest having fired both only playing Counter Strike or whatever the game is.
The H&K USP is a lot of gun in that its one of the largest frames out there and has what I feel to be an unwieldy grip circumference and trigger reach. That is only because my hands are not large enough to be well-suited for a 'bulky' large framed pistol. This may not be an issue for you. YMMV.
However, there are reasons H&K has a cult-like following among elite military and law enforcement units, while the Glock is considered a gun for 'the masses' (e.g. rank-and-file
officers who are likely to have never fired a handgun before their police training). Among those reasons, the ability to accessorize the H&K is unmatched. ;-)
The H&K USP Compacts are a perfect fit for my hands and certainly a better choice for concealment vs. the full frame. As for the Glock, well, I'm not particularly fond of the Glock Trigger, though its difficult to dislike the Glock because it is such a proven firearm.
Both guns are solid in their respective design and operation but have some differences which probably amount more to individual preference than anything.