I don't even think I have a least favorite Ayu album. I think it might be COLOURS and A One but I don't even kind of hate those albums at all. And you know, R'n'R Circus is definitely not on the top of my list, though I do feel it serves its purpose.
A Song for XX and NEXT LEVEL are actually near the top of my favorites. I think right now my absolute favorite album of hers is a tie between Duty, NL, and LOVEppears, though I just love (M)U, I am..., and RAINBOW.
I am one of those people who just...loves her music to pieces. Like, I can pretty much listen to any of her music. I only strongly dislike...like three or four songs she's ever done which are Teens, How Beautiful You Are, WARNING, and Sayonara, though I don't hate WARNING too much now.