The Sig 220 is one of the great pistols, up on the same podium with the 1911 and the Hi-Power. It is purely debugged technology, fiercely accurate and reliable as dirt. It's sole drawback is magazine capacity, which wasn't nearly the issue it is now back when the 220 was designed. They are fine, fine guns.
I'm going to take a pass on the HK 45...my friend Ken Hackathorn loves them, and in terms of use I spent a day teaching with a USP .40 and had no problems whatsoever, Still, it has been my experience that HK products for whatever reasons tend to have a bit more recoil than competing products. I suppose one could make a case that HK designs for various militaries, where perceived recoil is far less of an issue than it is in the civilian market (which HK tends to shun). Secondly, HK "customer service" is practically the punch line of a joke...I know LEOs who struggle to get spare parts.
I recently purchased an FNP45, not because I was dying for a new .45, but because the thing shot so well. It shoots "light," that is, perceived recoil is less than in equivalent guns. I like the choice between DA/SA and cocked-and-locked carry; trigger pulls in all modes was excellent. And it came with 3 magazines and a Blade-Tech holster with both belt and paddle mounting attachments. Plus — and here's the kicker — it is substantially cheaper than either the 220 and the HK. Something to think about.
Michael B