IMO, the Marriott Rewards program isn't a very efficient way to get airline miles unless/until you reach the levels of the travel package awards (approximately 185,000 points). That's a lot of credit card use (at 1 point per $) if you're not also going to be doing hotel stays. It does have a nice sign-up bonus (15,000 points plus a free night certificate) right now and also a referral bonus promotion going right now (if you have a friend who already has one, you might check into it).

I can't speak for the Starwood card, but I've seen many others on FT rave about it and especially its transferability; it may be a better bet for transferring into airline miles. I would recommend doing a search in the Starwood forum for more info on that program because I'm sure the merits have been discussed enough that you could be chastised for starting a new thread on the subject.