After a lifetime (literally) of carrying weapons professionally, I have Smiths, Sigs, Colts, and who knows what else in various safes and crannies. I have found out that Sigs are very good weapons indeed, however they hold nothing over 3rd gen Smiths, which are as good as they get. I even find myself packing a Smith auto in lieu of my all time favorite the Browning HP. I base my opinions on something simple, can I hit with it? I have retired my Colt Commander in favor of my Sig 220 SAO, but it has nothing on my Smith 45 autos. Not accuracy, not reliability, concealability, or anything else. And Smith customer service has it all over Sigs, by a furlong or so.
For a full size auto the Sig 220 and Smith 645/4506 are neck and neck, with an edge going to the Smith IMHO.
I was extermely sorry to see Smith stop making the metal frame guns, but the realities of the marketplace prevail over all of us.