Hi there welcome!!! Definately Dreams Cancun. My FI and our families went to Mexico a few months ago to decide between 4 places. Two of these were Dreams and Gran Caribe Real. Both resorts are beautiful in their own way.
GCR: Is a Vegas-style resort. The entrance is grand, the pools are huge, and there are sooo many rooms. It is also less expensive and still close to shops. The wedding coordinator was really nice, but I felt like she was searching for answers to my questions. Also, I didn't like any of the locations she showed us for the ceremony. Like many places in Cancun, they are undergoing beach recovery and there were several bulldozers and other big equipment there. As for the "rain plan", you have to decide the morning of the wedding whether you want to be outside or not; and the ballroom is EXACTLY like any other you've seen (and it smelled funny). If we're getting married in Cancun, I want to see the gorgeous views!!
DREAMS: when we first got to the resort I was dissapointed b/c from the outside it doesn't seem as grand. HOWEVER once you step inside it is amazing!!! Everything is kept beautifully and the view towards the pool and ocean from the lobby is awesome. Our WC Cecilia was great. She was answering questions before I even asked them!! When she showed us the different beaches we could choose, I started picturing our wedding. Once we got to the gazebo, we were all blown away!!! The view is indescribable....I knew that was the place we were going to get married! We continued our tour and I fell more in love with the resort. Everyone we encountered was so nice and it is located right on the tip so there are many shops around and you can see the rest of the coastline from the beach.
anyway sorry to go on and on, but just thought it might help
good luck!