Ole! Alegrias is one of my favorites. Reminds me of one of Diego del Gastors falsetas in C. Heard a recording years ago where he played Alegrias for 10 minutes or more using Am, C, and E. I always loved the transition from Am to C then to E. Very nice playing and well executed picato. C is a very pleasant key for alegrias.

Sam,
Thank you! I believe C is the most common key for cante accompaniment. E major has the most gravitas. The "happiest" key, often used for solo guitar, is A major (eg. Sabicas; Paco de Lucia; Nino Ricardo). Never tried it though.
Roland