Bourrée BWV 996 - J.S. Bach
The Bourrée is a lively dance from the Baroque period. This particular one is well known and liked, a sure crowd pleaser.
If there ever was a clear example of two distinct voices being present on the classical guitar, this is it. A great place to start would be to play each voice, the upper and lower, in isolation before combining the two together.
Not only musically rewarding but also technically challenging when it comes to left hand finger independence.