There are now 4 Royal Resorts in the Cancun Hotel Zone. None would be good for snorkeling. Cancun is known for its sand. Snorkeling is typically a 1/2 day trip/tour down to Puerto Morelos by van (~30mn) and a boat to the reef (just offshore), then it is excellent (friends report, I scuba dive).
The Royal Cancun (aka VCI), calmest water, but it is probably the most "isolated" from restaurant walking, but closest to the street where the public buses run.
For eating out, we just hop on the public bus, they run constantly and are on the street right out in front of the resorts. The resorts do run a shuttle between the resorts and their own restaurants.
That said the Royal Caribbean and Islander are up a hill from the road, it is a hike.
In my opinion, the Royal Sands would be the closest to walking to the most restaurants, we are not talking short distances, but walkable. Say a good 100 yards to get across its street, then 0.5 mile in both directions is a weeks worth of restaurants in the tourist area. Get on a bus, go to Cancun City and eat at a variety of places.
The Royal Haciendas, 45mn south at Playa del Carmen would have "the best" snorkeling (which is not saying a lot), but really no walking to restaurants to speak of from there.
