I'll list these based on how much I've enjoyed them but I don't see how any Westerns fan can put anything ahead of Gunsmoke. The longest series ever and in almost 800 episodes, the writing and acting were absolutely flawless. Not one single dud episode for 20 years and to be quite honest, the final season was the best, in my opinion.
Gunsmoke is in a class of its own.
1.) Gunsmoke
2.) Alias Smith and Jones - man, the writing on this series was unbelievable. You had to really stay with it or you'd get lost. Man, do I wish there had been more season!
3.) Maverick
4.) The Virginian (and the final season called The Men of Shiloh)
5.) Kung Fu - same thing, would give anything for another season or two.
I also love Cheyenne, Wagon Train, Wild Wild West, Big Valley so many other series. And as for Bonanza, as much as I loved it, there were so many oddities and so many silly episodes where they tried to be humorous and failed miserably.