The best time to go to Mexico is from the end of November to May. November in particular is a good time, as this is the transition month between wet and dry seasons – when the weather is still quite chilly and tourists have not started to flow into the country. It is also when the Day of the Dead is celebrated; some of the best places to view the festivities are in Oaxaca and Lake Patzcuaro.
Around Easter is also a good time to join in on local celebrations.
While June to October is rainy season, the weather is humid and the rains quite short, so those wanting to avoid the crowds could choose to travel then. Be aware that the Caribbean coast can also be affected by the hurricane season at this time.