Cava de Piedra (71 Mitre, on the square) - had my favorite humitas of the trip. They had a higher proportion of masa to fresh corn than humitas I had at other restaurants, and were consequently more tamale-like in texture (the other humitas were looser, like corn and cheese pudding). I tried both the salty and the sweet, and preferred the sweet. With spoonfuls of the house salsa on top (probably not the proper way to eat them, but the heat from the chile balanced the flavors perfectly), it's salty, sweet, spicy, and soothing and the same time.
I enjoyed the locro as well, but found it a little too salty. The people at the table next to me had ordered some items of the "high altitude" side of menu (predominantly nouveau Peruvian, featuring a lot of llama and quinoa) who found their dishes salty as well. I'm wondering if this is a regional preference, as I found most of the famed empanadas to be a little saltier than I'd like as well. Dinner with wine - $9 (American).
El Convento de Solar - I had a good tamale, and fairly tasty grilled rabbit. Conventional wisdeom seems to be that this is the best restaurant in Salta - my meal was good, but nothing really impressed me the way the humitas at Cava de Piedra did.
Empanadas - I can't say that any one empanada stood out. I had them from El Farito
(Caseros 509, on the square), La Cabana (30 Mitre), and Cava de Piedra. They're good across the board - small, freshly baked (no piles of precooked empanadas waiting to be reheated, which seemed to be the norm in Buenos Aires), but just a little too salty for me to be able to distinguish subtle differences between them.