Mexico:
Population 108 million, minus about 20 million that are up here.
Arable land: 243,000 sq km. That's about 450 people per square km, twice as much as the US, but nowhere near the problem that Pakistan or Tanzania has.
Life expectancy: about 75. Live births per mother, only about 2.39.
30% of the population is under 14, and there are 20 births per 1000 population, in the US it's 20% and 14, so they are having a few too many babies.
Per capita income: over $10K.
only .3% admit to having AIDS.
So I have to say, in the grand scheme of things, if you have to pick a place to live to ride out Oilmageddon, I would rather do it in Mexico than in Tanzania or Pakistan.
I think Mexico's problems are about 98% political. Their economy is run by a corrupt drug- or oil-fueled oligarchy, who are more interested in consolidating their own power and making themselves richer than in making their country more habitable. This has caused 25% "underemployment" and 20 million of their most productive citizens have chosen to chuck it and head north.
Having all of those young people up here keeps them from having the revolution that they need to straighten up the society down there.
CIA world factbook