Many locals think that this is the only place in Nazaré to eat grilled sardines. Enough said. When sardines are out of season, though (read: frozen), you can always opt for a different grilled fish instead. Stick to the suggestions of whatever is going that day.
Casa Pires started in 1930 as a small room grilling sardines and serving wine to fishermen. It's expanded somewhat, but still hauls in the crowds for its unpretentious dishes. And the quality, of course.