I've been a M-Th traveler for four years and I've found SPG and Marriott to be a winning combo. I like SPG the best, but sometimes it is either difficult to find SPG properties near the client site or the SPG properties are all sold out. Marriott has properties almost everywhere, even those small little towns where you hate to go. And if you're traveling every week, you can get plat status at both, no problem.
Of the 200+ consultants on my project, most all of them are either SPG or Marriott guys or both.