I got one with a 9.5 bbl. and absolutely love it. either of the two you listed would do fine. I guess it would depend more in the distance you are going to shoot at. The longer bbl will stabilize the round better for a longer range but of you are just going to do standard pistol (10-25 yds.) then you will be fine with the shorter one. I shoot at all kinds of wild distances just to see if I can do it but I'm also lucky enough to be able to walk out my back door and be abler to shoot at targets up to 200 yards. Maybe more if I really got bold...or crazy
The longer bbl might help you some with felt recoil. Shooting the one I have not is totally different then the Redhawk I had with a 7..5 a while back.
Either way you go you will love shooting it. you about have to love them to justify the ammo cost. There's just something special about shooting a Super Redhawk. Heck, about any of the Ruger wheel guns. They have been one of my favorite revolvers for years.