Mariscos del Atlantico (Puerto Madryn, Argentina)
In town for the whales, we didn't expect too much from the food in this tourist region. Turns out we were wrong. Our dinner at Mariscos del Atlantico was one of the best meals we had in all of Argentina. The grilled abadejo recommended by our waiter was amazing--I have rarely had such juicy, perfectly cooked fish anywhere. We also enjoyed the warm mariscos sampler, especially the super sweet scallops. If you're in the area, I highly recommend it. Make sure to call ahead for a reservation.
On the other end of the spectrum, steer clear of Mar y Meseta. We ate here our first night in town because Mariscos was full. Very mediocre for the price.