The music from the two shows is completely different. Nana is a punk rocker, Iwatsuki Rei played by Otsuka Ai is straight jpop and I enjoy both. Otsuka Ai does the theme song "Friends" for the series, but I prefer her version of "To Me" which she sings through out the show.
Both shows are about traveling to Tokyo and working hard to pursue your dreams, "Friends" adds two more female characters, all 4 have a dream, one music, one an art student, one to be an actress and playwright, and one who wants to marry an elite.
Nana is still ongoing 18 episodes out of a planned 50 have been aired and while "Friends" the series is finished the story was left up in the air a movie was released on August 12 in Japan. I can't wait for the DVD release to see ending to this engaging story.Link to Post