I recently switched to Quam and for me it's the best prepaid service: for 100 AR$ you get 1.5gig Internet, 100 minutes calls and 5000 SMS for 1 month. So far, everything works fine: they don't charge random stuff, recharging with an Argentine credit card (can be one of your friends) is super easy and the whole process is very straightforward (one can just recharge 500 AR$, which is added to your balance and every month they take 100 AR$ out and book a monthly package automatically.). Only downside is the internet speed, as it's Argentina...