Carrying cash and an ATM card is best; credit cards are also widely accepted.
ATMs (cajeros automáticos) are everywhere in BA and are the handiest way to get money; they can also be used for cash advances on major credit cards. There’s often an English-translation option if you don’t read Spanish.
There may be limits per withdrawal, but you may be able to withdraw several times per day – just beware of per-transaction fees. A fee is charged on ATM transactions by the local bank (not including charges by your home bank, which are extra). Note that this is a per transaction fee, so consider taking out your maximum allowed.
Notes come in denominations of two, five, 10, 20, 50, 100, 200 and 500 pesos. One peso equals 100 centavos; coins come in denominations of five, 10, 25 and 50 centavos, as well as one and two pesos. The $ sign in front of a price is usually used to signify pesos.
Don’t be dismayed if you receive dirty and hopelessly tattered banknotes; they will still be accepted everywhere. Some banks refuse worn or defaced US dollars, however, so make sure you arrive in Buenos Aires with pristine bills.
Counterfeiting of both local and US bills has become something of a problem in recent years, and merchants are very careful when accepting large denominations. You should be, too; look for a clear watermark or running thread on the largest bills, and be especially careful when receiving change in dark nightclubs or taxis.
US dollars are accepted by many tourist-oriented businesses, but you should also carry some pesos.
Many tourist services, larger stores, hotels and restaurants take credit cards such as Visa and MasterCard, especially for big purchases. Be aware, however, that some businesses add a recargo (surcharge) of up to 10% to credit-card purchases; ask ahead of time. Some lower-end hotels and private businesses will not accept credit cards, and tips can’t usually be added to credit-card bills at restaurants. Many places will give you a small discount if you pay in cash, rather than use a credit card.
Argentina’s unit of currency is the peso (AR$).
The Blue Market
In December 2015 currency controls were abolished, decreasing demand for US dollars on Argentina's 'blue' (ie black) market, but you'll still hear people on Buenos Aires' Florida pedestrian strip calling out 'cambio, cambio, cambio.' These folks are best avoided.
Bartenders Usually not expected.
Delivery persons A small bill.
Hotel cleaning staff A few pesos per day (only at upscale hotels).
Hotel porters A small bill.
Restaurant servers 10%; 15% for fine restaurants with great service.
Taxi drivers No tip unless they help with luggage; many people round up to nearest peso.
Tour guides 10% to 15%
Traveler’s checks are very impractical in Argentina, and even in BA it’s very hard to change them. Outside BA it’s almost impossible to change traveler’s checks. If you do decide to bring some, get them in US dollars.