Congrats and welcome!
It's easy to get lost in the sea of resorts out there - particularly Cancun. I did a bunch of research on that area as well and I have to say that Moon Palace is simply gorgeous and probably my favorite, but all three places are wonderful.
I suppose it comes down to what all you are wanting/needing. I know some places in the area do not allow outside photographers for instance. (I think Moon Palace was one of those.) Some do not allow children, etc, etc.
Anyway, I'm sure you'll find all the info you need here and you have lots of time!
Good luck.