It is HIGHLY recommended to bring cash to exchange while you are in Buenos Aires. The exchange rate for cash is much higher than the credit card/official exchange rate. There are multiple Western Union locations that allow cash to be exchanged easily. There is also a convenient business right in Palermo called PagoLínea (Address: José Cabrera 5001) For the current exchange rate see here - https://bluedollar.net/ The "informal rate" is the rate when exchanging cash for pesos. The "official rate" is the rate you will get when using a credit card.
Cards are accepted at almost every location! That being said, It is highly recommended to bring cash to exchange for pesos to use because when using a card, you will get a much worse exchange rate.
Uber is available in Buenos Aires and is quite easy to use! Be sure to change your payment method to cash in the app before using. Taxi's are also available and generally considered quite safe. Be prepared to use cash when hailing a taxi.