Glock or H&K: It's a toss-up
I have Glocks and I have an H&K USP45 full size - IMO, they are about equal as far as reliability, shootability, accuracy, durability, etc. The H&K USP45 full size is not a small pistol - it is about the size of a Glock 21 or a Colt Combat Commander 1911, although it is wider (thicker) than the Colt.
The one thing I hate about the H&K is this: The magazines are Godawfully expensive - $50-55 each, as compared to $25 for Glock magazines. All of the H&K autopistol magazines are plagued by hideously high prices; it seems like $50-55 is their standard magazine price, regardless of which pistol you are buying for.
The H&K auto is a totally different animal from the Glock; they are DA/SA with a decocker and thumb safety, which means you can carry the H&K in condition one (cocked and locked) like a 1911, if you want to, or carry it as a DA auto. One not so good "feature" of the H&K system is the DA trigger pull is HEAVY and long, although this may help to prevent accidental discharges when operating the pistol in DA mode.
Which is "better?" IMO, one is not really a better gun than the other, they are just different. As far as a full size autopistol, you can't go wrong with either.