The choice for the most part is 45 Colt or 44 Mag and Ruger or S&W.
Don't think S&W makes a Single Action. You also have the 454 Casull or 460. Both the 454 will allow you to also shoot 45 colt. The 460 will also allow you to shoot 454 and 45 colt. If you can afford it get a Freedom Arms in 454. If not consider a Magnum Research in 460