I am going with TEOM but Butterfly could take it some days too. they're very different records and I love both.
the fact that she almost never belts on Butterfly makes it feel more of a mood piece. a couple of the ballads don't do it for me but the suite in the middle with 4th of July, Breakdown and Babydoll is absolutely exceptional - classy, experimental, by far her sexiest music up to that point (and since). Close My Eyes is a stunner, and The Beautiful Ones might be her best cover. overall it's easy to see why she considers it her magnum opus.
on the other hand I just love that warm, 70s soul-aping sound present across most of TEOM. even the filler cuts (Joy Ride, Circles) are a pleasure to listen to because she sounds so good riding that production. and then of course the singles run is bulletproof and Your Girl is among her best album tracks ever. it pips it for me because the album ends on such a high note with FLAB (I don't acknowledge the platinum edition).
she's insane for having two albums of this calibre in her ouvre.