I don't really have any experience with Starwood, but so far, I am liking Marriott. Here are some things I have done to optimize my experience:

Platinum or gold challenge (Link to thread): If you think you can make either 12 or 18 nights in 3 months, call 801-468-4000 and ask to enroll in either the gold challenge (12 nights) or platinum challenge (18 nights). Note, they give you the rest of the current month PLUS three months to complete the challenge. So if you call today, you will have until the end of August to get the nights. The status kicks in immediately (within one or two days).

Marriott Rewards Visa (Link to thread):
Use this link to apply for the card - Marriott Visa and get 70K points, 15 elite nights (which do not count for the challenge), a free night certificate for a Category 1-5 hotel, and no fee for the first year.

Good luck!