Starwood points are easier to use: Cash and points almost always get you great value and the added benefit of getting an elite night. It's not difficult to get 3 or 4 cents per point, sometimes much more. With Marriott I refuse to get less than a cent a point, and just won't redeem at many properties. Paying 35K points for a $250 room isn't great value IMO.

Starwood 50 night Plat is actually quite easy: cash and points and points redemption's count, multiple room bookings count as well, as well as extra free nights etc. If you get both credit cards you get 10 nights credit.

The Starwood Amex card is much better for general spend than the Marriott Chase card, which I reserve for Marriott stays.