I'm no expert on Central America, but I agree that as nice as it is, Merida is too hot and humid. I would be more inclined to pick somewhere in the highlands, Guadalajara or nearby, Antigua or San Jose. San Jose has the advantage of the comparative political stability of Costa Rica.
Within the US, climate and politics are factors, as are the types of communities. I couldn't deal with the heat and humidity of Florida or the extreme heat of Palm Springs or Phoenix. Other places have their plusses and minuses. Face it, what the deal killers are differ from one person to another. Most big cities have enough positives to be persuasive, smaller cities become more problematic and subject to individual requirements.