Given the options you listed, I'd go with the blackhawk convertible; you can load 9mm with lead and use that in CAS as well as the 38 special or 357 (downloaded to 38 special levels). The large sdjustable sights will make it easy to get your POA and POI to match with your various loads. I would suggest sticking with the 4 5/8 or 5 1/2 inch barrels, as they are lighter and easier to get in and out of holsters than 6 1/2 or longer barrels. No real difference between blued and stainless, except price, of course!
Blackhawks are running less than Vaqueros and somewhat easier to find. They also are a better choice if you have plans to use them for other activities besides CAS, given the adjustable sights. They also would appeal to a different (and probably larger) resale market outside CAS if you decide this game is not for you.