I looove Cancun and it is a party spot, but I'm going to Mayan Riviera for the wedding for a few reasons:
1. The beaches at Cancun resorts are a bit small - it's hard to have a private ceremony.
2. Cancun is kind of Americanized - I wanted a more exotic atmosphere for the wedding
3. My favorite resorts in Cancun are pretty expensive
4. Mayan Riviera resorts are bigger - there's more to do onsite. And if anyone wants to go offsite, there are towns close to most resorts. (Playa Del Carmen is supposed to have a good nightlife)
LOL - this sounds like I'm a salesperson! But I really love Cancun, too and I had a hard time deciding - these are just the reasons that swayed me and FI.