Keeping this in consideration, is it better to use pesos or US dollars in Mexico?
The bottom line is, Pesos are accepted everywhere in Mexico! Many Mexicans make it easy to use Dollars and this certainly makes it easier for many tourist that come to Mexico. You will however make the best use of your money if you exchange it and use Pesos.
Also, how much pesos should I take to Cancun? For All-Inclusive trips we bring about 1500-2000 pesos or so for tipping per week, plus maybe another 5000 for tours, shopping, day trips-IF you will be doing any of that. I agree the best way to get pesos is once you are in Mexico, with your ATM card at an ATM.
Similarly, what's the best currency to take to Cancun?
Pesos
Is $100 a lot of money in Mexico?
At current exchange rates, $100 USD is around $1,900 MXN. For some people in Mexico, $1,900 pesos is quite a bit, but for others, not much at all. Mexico is not really a poor country. There is a lot of poverty here, but there are also a lot of people who are quite well off.
