Yes, you are right, they are a bit bulkier than I would like. Because of the bulkiness, finding an IWB holster was a real chore. Right now I am carrying a G19 because my USPc holster is in for repairs.
The reason I chose HK is as an earlier poster said, reliability and durability. I also like the configurations available. I have not shot a LEM trigger much but will probably try that out more in the future. I don't think I would change any of my USPs given my current experience.
As to durability and reliability, I have witnessed many Glocks in action and they have earned my respect in this arena. They are absolutely reliable as long as you have decent ammo and a decent grip. I have never seen a HK or a Glock malfunction except for pilot error type of malfunctions (limpwristing mainly).
All my USPs are V1 so that I can safe the pistol for when I am driving and I need to unholster or stash the pistol in the console, between seats etc. I am much more comfortable being able to engage a safety for this situation which is fairly common for me.
With a Glock, I would need to place it in a hard-sided holster or case to make certain there would be no chance of catching the trigger on something.