Thalia
Why? = "Regresa A Mi", "Entre El mar y una Estrella", "Tu y Yo", "No ME Enseñaste", "I Want You", "A Quien Le Importa?", "Baby I'm in Love", "Cerca de Ti", "Amor a la Mexicana", "Seduccion"
I have to go with Thalía in this one. Paulina may have the catchier songs (and songs that are most likely to be guilty pleasures), but Thalía is by far the better singer and performer.