Chichen Itza is great, the main pyramid is very well preserved and the whole area is filled with very interesting ruins. As the previous poster said it can get really hot there, so be prepared.
We also went to Cobà three years ago and while the pyramid there is in worse shape than CI you can still actually climb it which makes for a very different experience. Once at the top the view makes you feel like you're lost in the jungle. We really enjoyed it. Tulum is the closest one to Puerto Morelos, if I remember correctly. Very beautiful place, the view of the ruins against the sea background is fantastic. It was also very hot when we visited, and there is no shade to speak of, so don't forget sunscreen and a hat.
In all three cases we chose to do the visits while staying at a vanilla resort nearby. Leaving Desire is heartbreaking enough, no need to do it twice in one stay.