USD Cash exchange: Most likely you will get a better exchange rate if you bring USD and change it to Argentinian Pesos (ARS) in exchange offices in the street. As you may know, there are different types of dollar exchange rates in Argentina due to several government restrictions. For your reference, the exchange rate for tourists should be around 1 USD = 480 if you change in a local agency on the street. Importantly, brind USD cash bills of 100USD, as these are the ones you will be able to change in the street. Lower value bills may not be accepted. Avoid bringing other currencies (like Euro or Yuan) as these may get a lower rate or may even not be accepted for exchange.
Credit or debit card: In Argentina you can use your credit or debit card to pay in most places, and you should get a good exchange rate due to the new regulations (the value should be close to MEP Dolar type of exchange). However, since this may also depend on the type of card you are using, in order to confirm this, you can make a small payment and check the conversion rate you get just to be sure. According to VISA website, if you pay with VISA, you will get this exchange rate immediately. However, for other cards like Mastercard, it may take a few days until you get a reimbursement in your account that matches a good exchange rate. For more information about the benefit for: