What is the Best Hotel Rewards Program? What do you recommend? I wanted Hilton because you can choose your own house
Hilton has certainly stepped up their game in Las Vegas. You can use or earn Hilton points at Virgin Hotel, Hilton Vacation Club (tucked away in the Planet Hollywood mall), and the Resort World properties. Oh and I almost forgot that the Waldorf Astora is also connected to the Hilton family and you can stay there. The Waldorf is the old Mandarin Oriental.
As for Marriott, you pretty much have to stay either off strip or there is a Marriott Vacation Club/Timeshare location across from Planet Hollywood. Cosmo used to be a part of their loyalty program with the premium hotels class but I don't think so anymore. Sahara / SLS did have a partnership with the W hotels but I don't think so anymore either. So it might be tough to stay on the Vegas strip on the Marriott program. I think there is a new hotel, the Fountain Blu or something that was at one point owned by Marriott.
Wyndham hotels seem to have good ones. I have never participated in something like this so I wouldn't know what to compare it to but La Quinta Inn & Suites, Baymont, and the Travelodge are a few of their places in Vegas that participate in the rewards program.
I love the Marriot rewards program. I stay a lot and have a lot of points collected now. They also have locations everywhere so I can usually find something for any price range.