Although Ritz Carlton is under the umbrella of Marriott, they each have their own separate rewards program. Although you can freely switch between Ritz Carlton and Marriott Rewards programs, you cannot belong to both.
Although Marriott is not having a summer promotion, I did find out that Ritz Carlton is currently having a promotion that runs through September 30, 2015.
You will receive 30,000 bonus points for staying 5 nights at any eligible Ritz Carlton property, and an additional 40,000 points for staying another 5 nights. The promotion is capped at 70,000 bonus points. This is not as lucrative as last year’s promotion in which you could earn up to an extra 100,000 bonus points. Factoring in the spend factor, that would have resulted in enough points for two free nights at any Ritz Carlton property in the world.
The earning and redemption rates are completely the same between Ritz Carlton Rewards, and Marriott rewards so is one better than the other? On the surface, it would seem like they are the same program with different names. The benefits are exactly the same.
I would choose being a member of the Ritz Carlton Rewards program, since you are eligible for both Ritz Carlton promotions and Marriott promotions, while being a member of the Marriott Rewards program limits you to Marriott promotions only.