I have two non-1911A1 .45 ACPs: a Sig P-220 and an H&K USP Tactical. Both are truly excellent handguns.
The Sig is a splendid firearm: accurate, reliable, beautifully designed and manufactured. I simply cannot laud the P-220 too highly.
The H&K is new (less then a month old), so my evaluation is less certain. It, too, seems to be an outstanding semiautomatic. Just today, I fired a hundred rounds of 230 grain FMJ through it with zero jams, misfires or any other problems. Its accuracy is excellent -- perhaps (??) not quite as good as the P-220's; however, I am still getting used to the H&K and it may turn out to be even more accurate.
In sum, both the Sig P-220 and the H&K USP are superb .45 ACPs. You simply cannot go wrong with either. I would select the one that felt more comfortable and was more accurate for you.