okc, 6/3/12
I have both the HK-USPc .45 and the Sig p245 (the earlier version of the 220c). Both are fine pistols.
Sig 220c (p245)- accurate, light and reliable. It conceals well. Trigger is good in DA and SA. Magazine prices are reasonable and it will take its own 6 round mag and also the full size 220 8 round mags. It is my primary carry .45 pistol.
HK-USPc .45- accurate, light and reliable as well. The grip is longer than the 220c because it holds 8 rounds in the mag instead of the 6 in the 220c. Despite the longer grip it still conceals well. The DA trigger is terrible- long, heavy and stacks severely before the trigger breaks. The SA trigger is average. Mag prices are usually over $50 each. This is my primary sidearm when I go hiking or hunting as it's easier to clean all the sweat and dirt off the polymer frame than the 220c's aluminum frame. It's a good gun but not worth the extra money that it costs over other quality polymer framed pistols.
As with all purchases you need to handle and fire both options to see which fits you best. Good luck.
best wishes-oldandslow