Can’t go wrong with either, both the Smith and the Sig are good guns. In my opinion, the Sig is the ‘better’ gun. It’s a more refined/better engineered, smoother gun. Only drawback is the mag capacity, but unless you’re planning on going into combat, does it really matter?
For collectibility, you can’t beat the Smith, and while I don’t own a Gen 3 10mm, I’ve shot a couple and they shoot great. I just think that Sig did a great job with the 10mm 220, they’re very well made guns. My friend has one, and I’ve shot it a few times, it’s a beauty.
I do own a Smith 645, and love the gun. 100% reliable, accurate, and a beautiful chunk of metal. Also own a P220 in .45acp, gun is flawless, great design, and very accurate. For 10mm, I’ve got a Glock 20, Glock 29, Colt Delta, and a double stack Rock River 1911. Like all of them, but that G20 is a heck of a platform for 10mm.
When I ever run across a Sig 220 in 10mm, or a Smith 1006 in the wild, I’m buying it, whichever I find first…