Following a perceptive query from Kevin Drum, I bought and sampled sour creams from El Salvador, Honduras, Guatemala, and Mexico, all from my local Mundo Latino supermarket.
The Honduran cream had a taste and consistency somewhat like that of the El Salvadoran cream. Yet the cream from El Salvador was sweeter in a nice way; this came more to the fore when each cream was combined with a tamale. The Guatemalan cream tasted noticably worse than either — flatter, heavier, and less tart/tangy. Its label indicated it had a much higher level of saturated fat and cholesterol.
The Mexican cream was different altogether. One Kevin Drum reader commented:
Mexican crema is yellowish and buttery. Salvadoran is whiter and tangier. American is lighter, firmer and more yogurty.
Of the creams from El Salvador, the best ones are in the small plastic bags, not the plastic containers. If you have the feeling you don't know how to store the thing once you open it, that's the one you should buy.
Those are the supermarket brands. The very best sour cream I've had was in Nicaragua, where the poverty and underdevelopment have kept the food supply chain shorter and fresher, albeit at the cost of higher food prices relative to real wages. San Salvador has much more fast food than does Managua, for instance. But they don't have mass produced Nicaraguan sour cream in my local supermarket, perhaps because relatively few Nicaraguans live in northern Virginia.