Hmmm... I would keep the USP 9mm compact and the Sig 220... Here are my reasons... I would choose the USP over the S&W for conceal carry. I just feel that it would be the better choice for that type of work - more durable/rust resistant gun, better caliber, in my opinion, and more comfortable to shoot, also in my opinion. If you can't conceal carry, but just want a small gun, I would still choose the USP - cheaper ammo, easier to maintain, more durable.
I would keep the Sig 220 since that would seem like the most accurate and most refined gun of the three, in my opinion of course! Plus I feel the Sig can be a better home defense gun or target shooter than the other two guns listed...