All three are available at my local mexican market. How are they different? 
The primarily difference is where they are made.   But there's also a play on its acidity. Kind of like milk vs. buttermilk or different types of plain yogurt. I always thought of El Salvadorian crema was more acidic for my tastes. I think of Honduran as a less acidic, more creamy taste and I really enjoy it.  