Tastes great, less filling. Both are good guns.
The Smith is a bit cheaper, and you can switch barrels. Downside- aluminum frame. If you go with the 22A, get the 5.5 inch barrel. Balances much better.
The Mk III has a frame mounted mag release, unlike the earlier ones that were "toe-of-the mag" releases.
You pays yer money, you takes yer pick.