This post looks familiar...dig a few pages in and youll find my post asking the exact same thing, with results from many.
In the end I went with the USP. Lifetime warranty, utter reliability, just as accurate as the Custom II (arguably) and it doesnt NEED modification...but if you want, drop in barrels (threaded or no, O-ringed tactical style, see CCF), adj sights, night sights, new grips, etc are all available for it. It fits my hand fine (.45 Fullsize) and will eat any ammo you feed it.
The kimbers had lesser quality control IMHO...seems like some come from the factory running like a top, and some dont. Also keep in mind that the USP is a combat rated weapon, with looser tolerances (but not of lesser quality) than the kimber. Youll have to clean alot of 1911s more than you would the USP before you start getting jams. In my oppinion the Kimber makes an excellent CCW/home defense peice, but dont try to carry it 14 miles through mangrove swamps or snow and ice, etc etc etc...my HK sits on a thigh holster, not a CCW holster. I depend on it to kill something that threatens me after ive hiked through streams, snow, and mud. That being said, I still want a kimber eventually to take to the range/for CCW. I love them 1911s, just dont trust most of them to go bang everytime.