My first semi-auto pistol was an original Chiappa 1911-22. My son and I shot thousands of rounds through it over the last three years. I sold it this past weekend and used the money to pay for part of a Smith & Wesson M&P 22. He was a little miffed at me for selling "his" .22, but after shooting the M&P, he feels a little better about it.
When I originally purchased the 1911-22 I was looking for a Browning Buckmark, but I saw the Chiappa sitting next to it, and it just called to me. Compared to the M&P, it's heavier, but it shoots just as well. The Chiappa came out a year before the GSG, and if I were looking for a 1911 style .22 today, I would get the GSG. It is built a little better than the Chiappa, but that would also make it a little heavier too.
So far, I like the M&P better than the 1911-22 because it is lighter and has a better trigger. If your heart is set on a 1911 style pistol, go with the GSG, but keep the M&P in mind for when you want a change (or when your arm gets tired).