Unless you're going to really tiny villages, any bank ATM will give you as many pesos as you need when you need them. You can minimize fees by making fewer large withdrawals rather than more small ones, but as a fraction of the cost of your trip, even doubling the amount you pay in ATM fees will be insignificant. Ask yourself: Would I have planned this trip any differently if the air fare had been $20 more? If you answer that with "no," why freak out over the same $20 when it shows up on a different line of the same trip budget?
Do people use traveler's checks any more? For all practical purposes, no. Totally replaced by credit cards and easy access to cash via international ATM networks.