We were in remote areas in Salta and Catamarca just a few weeks ago. I was using Claro and our guide Personal. She swore that Personal was the best for that region, but there wasn't a single time that she had service when I didn't and vice versa. In the puna, service was very spotty to nil while on the road, and everyone seemed to rely on WiFi in the hosterias. In larger towns, such as Cafayate, and other places along Route 40, service was more reliable.