I was unsure about the USP45 at first. I was going to get it regardless, but it seemed so big. I've found it to be a great gun. I can conceal it fairly easily, but if it's gonna be a hot or long day, I'll take the G30.
A buddy of mine has the Sig. I really like it but it's not something I would buy. One of the selling points of the HK was mag capacity. I believe the H&K is also lighter and thinner. There are so many versions now that to compare you'd have to be specific. Honestly I'd try to find a 1911 first.
Either way I would consider these 2 pistols more along the lines of a battle pistol. I've heard rare reports of issues with either.
As far as the H&K compact goes... It's a good gun for concealed carry. Here are some numbers to crunch:
Description___caliber___weight____length___width___height__capacity
usp45f _______45 _______20.16?____7.87___1.26____5.55___12
usp45c_______45________23.52?____7.09___1.14____5.06____8
g30__________45________26.49_____6.77___1.27____4.76___10
Kahr p45_____45________18.50_____6.07____1.01 ___4.80____6
I know you asked about specific makes, but this helps put it all into perspective. I saw so many variations on the Sig that I left it out. I have little doubt in the glock, but p45 seems to still be going thru some bugs.
Feel free to correct any mistakes there. There's gotta be something wrong with the weight on the usp45f.