Ruger. I have a bunch of Ruger single-action revolvers, and am most happy with them. I have 2 Super Blackhawks and a .41 mag Blackhawk I bought in 1987, have put thousands of hefty handloads through them, and they are still as accurate and sturdy as new. For other calibers, I have a bunch of .45 Colt Blackhawks and Vaqueros, .22 LR Single Six's, and have shot them enough to wear out most other guns, but there is no sign of any trouble with them.
If you are wanting it for Cowboy Action Shooting, Ruger Vaquero's were designed for that. Ruger also makes some black powder replicas that might be fun.