Easily for me it is Malagueña. Here is where it gets a little more interesting. Most folks on guitar forums associate it with Spanish guitar. It was actually written by Ernesto Lecuona, who was Cuban, not Spanish. Further adding to the confusion is the fact that Malagueña translates literally to woman or girl from Málaga, the city in Spain. The other interesting thing is that Lecuona wrote it for piano, not for guitar. However, some smart, creative flamenco guitar players in Southern Spain realized that the piece lent itself nicely to the flamenco style. Not surprisingly, my favorite version of Malagueña is flamenco legend Sabicas' rendition. Not far behind is Mason Williams' Classical Gas. What a great piece of music!