I agree that this is the hardest decision... took me several weeks!
A few questions...
How many people are you expecting to attend?
Do you want a small location or large?
I will tell you a few of the places I looked at in the RM:
JW Marriott - nice wedding gazebo
Marriott Casa Magna - same gazebo, guests could stay at either hotel
Hilton Cancun - modern decor, nice pools and beach area
Playacar Palace- in Playa del Carmen, modern decor, all-inclusive, smaller than the other resorts I mentioned. I really wanted to have it here but we had too many people planning to attend.
We finally decided on Dreams Cancun... after trying to stay away from AIs due to price, and wanting to give our guests choices... it really is the best option for us. It has a beautiful gazebo that overlooks the ocean and has so much to offer our guests. It is kid friendly that is important to us as there are several little ones attending.
I actually put together a spreadsheet with ALL the hotels in Cancun and the RM and looked through the visitor pictures and hotel pictures from Trip Advisor. I made note of the prices during that time frame if given... some were not posted yet, what was included, what the wedding packages were, something that stood out of the pictures that I would be able to remember, and then if I really just didn't like it at all I greyed it out. Once I narrowed it down to about five, my FI and I went over the details of each. We had both really liked Dreams from the beginning.
We had a few factors that made us move the date to early next year. So I sent s few dates to their WC, she told it was available and we had a location and date that was a winner!
This really is a hard decision, you will find many threads about it here. Tammy(host) has information on many resorts in the RM listed here to assist in your decision making.
Good luck and let us know (other than throwing the dart for you) how we can help
PS: I am in Columbus Ohio.