A1/A2 have all the classics
A3 I never got into
A4 has Faint, Junai no Crescendo and Only Today, but also some of my most disliked songs.
A5 has the modern classics; Kuroi, Hagavi, Tsundere, Sanjou... yeah I'm voting for this.
A6 is still pretty unknown to me. First watch was good, not I didn't get addicted to it.