Perhaps the best reason I give for booking a wedding in the Cancun Hotel Zone, as opposed to Riviera Maya/Playa Del Carmen is that your guests will have options and freedom. The options and freedom go hand in hand because what you find in the Hotel Zone as far as great restaurants, shopping, entertainment, bars, clubs, etc., etc, you will not find in the other places you are considering. This is not to say that the resorts offer many amenities in Riviera Maya, but Cancun as a whole offers much more. If you decide on the Hotel Zone as your destination, your choice will be made easier, so first I recommend you consider area first, then narrow it down to resorts. That's my dos centavos.
212eric