I own both a Sig P-220 and a stainless Kimber Custom/Classic full-size 1911A1. Both are absolutely excellent semiautomatics.
Despite all the "Kimber bashing" I've read on TFL during the last few months, my pistol has been unbelievably accurate, reliable, and was clearly manufactured to exceptionally high design/quality standards for materials, machining, fit, finish, and operation.
The Sig P-220 is also very accurate (almost as accurate as the Kimber) and has operated flawlessly -- not one problem in thousands of rounds. It, too, has outstanding design, material, and manufacturing quality (probably equal or better than the Kimber, except it is not a stainless steel design).
You should consider eventually buying both semiautomatics. If, however, I were compelled to purchase only one, it would be the Sig P-220 because I believe it is slightly more reliable, which can be crucial in concealed carry and defensive situations.