I have both, and like either, or ... Both are good in they're own way. I find the older guns have a smoother cocking action, but the new ones are more rugged when it comes to internal parts, and with a transfer bar safety you can carry 6 rounds safely (but silhouette shooters shoot in strings of 5).
If something does break (which seldom happens) it is easier to find replacement parts (and acessories) for the new model then the old.
I've been shooting the big single actions since the 1950's and have grown to like the earlier style, but this shouldn't mean a thing to you.
I would observe that the old models are becoming more and more established as collectors' items, but this in no way detracts from using them for silhouettes. It does make them good investments though ...
Edited to add. The Super Blackhawk has the Colt style "plowhandle" grip, and when you shoot a heavy load the gun tends to roll up in the hand (which it is supposed too do), but with a long barrel at long ranges this can cause vertical stringing of your group and result in high over-the-target shots. I suggest that you consider a Bisley/Blackhawk. It is the same gun as the Super Blackhawk, but with a different style grip and hammer. The shape of the grip tends to reduce or eliminate the virtical stringing problem.