Depends on how often you travel and your ability to stay in the future:

If you don't travel much and/or not at Marriott, I would join and earn miles. You earn 3 miles per dollar. So, assuming you spend 7 nights at $100 you would earn 2,100 miles. Plus, you'd earn miles for $ spent on breakfast, phone calls, etc.

Marriott is running a double points promotion with Visa, but it only starts on your second stay. So, you would probably want to make a 1-night stay somewhere first. You would then earn 14,000 points for your stay. To earn double points, you have to register at 800/442-9929 or their website.