La Biela is a historic cafe in front of the Recoleta Cemetery. It's one of the most popular spots here and the location is the clear reason. It's hard to beat the outdoor dining here, with views of the cemetery and plaza in front.
But, I do have to admit I find the menu to be overpriced thanks to its location. Better cafes (La Rambla on Posadas nearby) and better empanadas are to be had elsewhere.