My Mexico travel has been limited. That said, I stayed at Las Mañanitas in Cuernavaca for a few days. It is a beautiful hotel and the restaurant is considered one of the best in Mexico. The restaurant is on a terrace in a garden setting. The breakfasts and dinners were all wonderful. Las Mananitas Restaurant
I've also spent a few weeks the past two years on Isla Mujeres, a 20 minute ferry ride from Cancun. Isla is everything that Cancun isn't, meaning I love the place. Partly for its laid back way of life and partly because the restaurants are consistently good to great.
My favorite Isla Mujeres Restaurant, is a very basic home cooking place, La Lomita. Two dishes I will never forget - their chili rellenos, their chicken mole (spectacular mole sauce). Both the best I have had anywhere. I want to taste the Mole sauce Rick Bayless did for Top Chef Masters just to see if it is as great as La Lomita. Isla Mujeres Restaurants including La Lomita