My vote is for Marriott for two reasons:

1) Number of locations. I travel to some obscure places (El Paso, TX and Greenville, SC just to name two) and if I was with Starwood I would be SOL.

2) The quality of Marriott's properties, although I wouldn't use the word consistant to describe it, is superior overall to Hilton and the Sheraton line of Starwood. I have stayed at some nice Hiltons and Sheratons but there are a lot of dumps out there. I'm not claiming every Marriott property is gorgeous but overall the level of quality is superior.

The clincher for me is I can use my MR points at RC. I stay with Marriott for business and use my reward points at RC and some of the new JWs.