We like the Ren for its location as referenced above. Never stayed at the Marriott as yet, but might this summer before our cruise. I've got reservations at both right now and will have keep checking the rates.

Its close to the Central Station and the Tram Stops are just a short walk away. The trams in Amsterdam are quite good and we never have any problem getting out to the other areas for visits. We especially like being able to walk over to the main street for some Frites.