One thing I like about carrying my steel 1911 vs my poly M&P is if I ever need to use the gun as a bludgeoning device, the 1911 is much better suited for that task. I wouldn't want to get hit with either, but the weight of the 1911 would make it much easier to knock someone unconcious.
In regards to the Sig, two things I don't like about them. 1. External extractors (not what the 1911 was intended to have) 2. Dimensions are not normal 1911 dimensions so holsters can be tricky to find.