In my limited experience, local ATM withdrawals incur a usage charge, on top of which the conversion rate will not be competitive.
Credit card transactions will incur an additional charge (cross-border handling fee ?) and the conversion rate will not be competitive.
If you want the best rate, shop around and take all you need in cash and don't use a card. But that is a high risk choice so you should mitigate risk by accepting the inevitable transaction charge / FX rate annoyances and only take as much cash as you need for cash transactions; use card for the bigger value transactions.
If I were going over, I would bring enough cash for out of pocket expenses and charge all shopping, restaurants, etc. to the credit card.