The RC is right next to the Westin. And the RC there is very nice, much nicer than the Marriott (though it will be more points/cost as well.)

But I think the latest question was really about the CM Cancun. I can't really speak to it as I've never stayed there, but there is a CM Cancun master thread: http://www.flyertalk.com/forum/marri...rt-mexico.html