I can't comment on Puerto Vallarta but I love the Mayan Riviera for so many reasons! First and foremost the Mayan Riviera is very affordable with many options from budget hotels to luxury resorts. Food and drinks is great, in my opinion much better than the DR or Cuba. Countless activities are available from visiting the ancient ruins of Tulum to ziplining, horseback riding, snorkeling, catamaran cruises etc. 5th Ave in Playa del Carmen is a whole experience in itself with all of its restaurants, bars, shops and of course Coco Bongo's.
The people are absolutely fantastic as tourism is their main income they are so helpful and friendly. Money exchange is easy with almost every place accepting USD (Tulum Ruins is the only place I can think of that only take pesos). The Cancun airport is large and sees a huge volume of flights daily so it should be fairly simpe for your guests to get direct flights in and out of the country.
On the downside the beaches are not as great as say Punta Cana in the DR, there is a lot more coral but are beautiful to look at and the water is warm! Also to make your marriage legal in Mexico you must arrive 4 business days prior to the ceremony and have blood work done. Because of our flight schedule we opted to a symbolic wedding in Mexico, arriving on a Friday night and getting married on Monday, things couldn't have been easier. We met with the wedding coordinator on Saturday morning to go over the details and then enjoyed ourselves until Monday - no blood work, paper work or passports required.
To narrow down the huge lists of resorts in the Riviera you should ask yourself the following questions:
How much do you want your guests to spend?
Large or Small Resort?
What amenities do you need at the resort?
How long of a drive are you willing to go from the airport?
I have stayed at the following so if you have any questions about these resorts in particular let me know.
Grand Sirenis twice
Gran Bahia Coba
Grand Sunset Princess
I also stayed at a resort in Cancun (I think it was a Barcelo) which I enjoyed but I prefer the Riviera.
Congrats & happy planning!