I've owned a GI Mil-Spec, Kimber Custom Eclipse II, the Glock 21, and a couple HK's.
-Mil Spec-
Hated the sights. Didn't feed hollowpoints. Only gun I've ever owned that developed surface rust (my fault, but from then on I went for more durable finishes).
-Kimber-
Beautiful piece. Fed everything. Great trigger. Satin Nickel finish that looked and held up very well. No problems with this gun. Expensive, but worth it to me.
-Glock 21-
Went bang everytime. Ate everything fed to it. 13+1 capacity. Can be stripped and given a basic cleaning in less than 15 minutes, even when extremely dirty. Grip angle wasn't right for me, but other than that great gun.
-HK USP .45 Compact-
Expensive, but I've never been happier with a gun. Holding it in my hand feels like it was built for me. No problems so far (it's still relatively new to my collection, only about 1000 rounds through it). As easy to maintain as the Glock was. Ambi mag release is faster to operate for me than the traditional variety. Best of all, I can carry it C&L style and enjoy the single action trigger.
Of the .45's you're considering that I've also happend to own, HK was the best for me. Naturally YMMV, but I can promise you you'll have fun figuring it out if you get a chance to try them all! Good luck.
