Withdrawing from an ATM is not a great option because the amount you can take out is absurdly small - when I was there in July, something like $25 per transaction. They've started introducing larger bills, which in theory might make using an ATM easier at some point - but I wouldn't bet on that anytime soon.

The best way to exchange money is to bring crisp, new US $100 bills and go to a trusted place to turn them into pesos. If you stay in a hotel, the staff should be able to recommend someone, and many (although I don't think all) Western Union locations will do the exchange for you as well. You just have to shop around. While it seems like a sketchy process, it's really not - just use common sense and get a recommendation for where to go.

The second best way is to just use your foreign credit/debit card. You'll get a somewhat worse exchange rate, but it's much more convenient.

I don't recall seeing DCC offered in Argentina, although I only used my cards for purchases a couple of times and once at the airport ATM when I landed, as I just needed a small amount of cash to top up my Sube card for the bus into town and get a bite to eat.