Generally I like to go by director when it comes to Westerns (works for Noir too), since lots of them did more than a few back in those days when contracts were the norm. Of course you have the giants John Ford or Sergio Leone, but I’d put Anthony Mann at the same level (Man Of The West, Winchester 73), or Peckinpah. Nicholas Ray, even though he did fewer Westerns, has to be named if only for the masterpiece that is Johnny Guitar (Run For Cover is décent too).
Boettincher is a great example of a today less heralded name but who did some great work. Delmer Daves is up there too