I would think that Harrah's would lead the way in drying up room offers......but you just never know.
I would think they are the most dependent on getting players back in the door time and time again through offering free rooms. They have historically been the most generous with room offers, and I think they understand that bodies in beds = $$$ for them, through gaming revenue, dining revenue, shows, etc.
In terms of comping policies, I think CET is actually the smartest in Vegas. I would also think that MGM would stop comping before CET just because MGM tends to offer a more premium product and likely attracts a higher-end clientele overall, who are less sensitive to room rate.