flyastrojets: There are lots of threads both here and in the Starwood Forum that compare the two chains.

I love Marriott for its consistency and ubiquity. I have rarely had a bad stay and I have had numerous fabulous ones. I also think they have great employees. One thing no one has mentioned yet in this thread is the high thresholds for attaining status. Marriott is the toughest to achieve. That's great if you stay enough to be platinum (less dilution of benefits). But, if you are traveling on your own dime as I do it's a struggle to make gold.