I've stayed at the JW Cancun twice and the Marriott Cancun once over the past couple months. I also spent a night at the Westin Lagunamar. Elite recognition is pretty slim at both the JW and Marriott.

The JW recently underwent a renovation last year/earlier this year. The rooms are nicer and more up to date than those at the Marriott. The times we stayed there were on higher floors. But it seems like all of the rooms at the JW have some sort of view.

The Marriott is currently undergoing a renovation. So there's a steady amount of construction going on. A fair amount of noise. Elevators being out of service. Some of the "partial ocean view" rooms, especially on the lower floors barely qualify as that.

The Marriott is cheaper. I've seen recent rates as low as $120/night with taxes included. The lowest rates at the JW have been about $40 to $50 more.

No matter which hotel you are staying at you can use the amenities at the other property.