If I may also give my opinion
?
Anyway, IMO, you should really check these albums out:
MY STORY
(miss)understood
Secret
GUILTY
Of course these are her most recent albums.
But uhm, you could also download A BEST (first best album), A BEST II -BLACK- (second best album with the "dark/sad" tracks) and A BEST II -WHITE- (second best album with all the "genki" songs)