This is tough. They are both mediocrity at its finest. I may have to go with Demi though because the trinity of that album - Without The Love, Two Pieces, & Nightingale are stronger than Miley's trinity - 4x4, #Getitright, & Maybe You're Right.
Bangerz, and it's not even close. Demi was a good album when the music well was dry but since she's released, it's clear every and any girl in her age group can and will put her to shame this year.
Demi's got a great voice but Demi (the album) is lacking severely.