Although one is on top of the music world and the other is struggling to make a comeback, pop divas Rihanna and Christina Aguilera have one crucial thing in common: Neither one has ever established a consistent musical identity, which means probably half the songs on their respective new albums (Rihanna’s Unapologetic, Aguilera’s Lotus) could have been recorded by either one of them.

Aguilera has the stronger voice, certainly, although much of Lotus finds her either abusing her talents (by over-singing on overwrought ballads) or obscuring them via vocal effects. Aguilera even mimics Rihanna’s trademark staccato vocal style on “Cease Fire,” but as with 2010’s Lady Gaga-biting Bionic, emulating the reigning pop queen isn’t going to put her back on top. Lotus is best in its first half, with bubbly, catchy pop tunes like “Red Hot Kinda Love” and the Max Martin one-two punch of “Your Body” and “Let There Be Love.” But Aguilera isn’t content to just take a snappy hook and sing it well, and Lotus suffers from the same inconsistency as Bionic.

Unapologetic, Rihanna’s seventh album in seven years, is similarly all over the place, ranging from middle-of-the-road pop single “Diamonds” to drippy piano ballad “Stay” to dubstep-infused club numbers “Jump” and “Right Now.” It’s hard to imagine anything uglier than a duet with toxic ex-boyfriend Chris Brown titled “Nobody’s Business” that includes the line “Let’s make out in this Lexus,” although Rihanna’s vocals are as disengaged on that song as they are on the less personal tracks. Aguilera might be desperate to show off her vocal range, but at least she sounds like she has something at stake.