Cain vs. Abel. Foreman vs. Ali. And now, Brandy vs. Monica. Well, “The Boy Is Mine” is the most successful single of the year–indeed, the most successful female duet of what chart geeks like to call “the rock era.” And if the matchup doesn’t quite qualify as historic myth, it certainly works as music-biz metaphor.

The duet was conceived for 19-year-old Brandy Norwood’s second album, Never Say Never–a Bondlike title that aptly evokes the secrecy, intrigue, and multinational interests now underlying all such pop power plays. As the widely reported story goes, Brandy first extends the duet invite to 17-year-old Monica Arnold to quash rumors of their rivalry. Monica accepts, but only if they split the take 50-50.

In May, the song drops and blows radio, video, and retail the fuck up. But the rumors quickly start again, and how could they not? Did Monica and Brandy really expect a song about a fictional rivalry to hush talk of an actual one? Brandy’s pissed because Monica put too many vocal runs in the song. The braided one then performs the song by herself on The Tonight Show. Monica fires off a statement to MTV that Brandy’s solo performance “hurt our song.” Meanwhile, Brandy’s off on the sneak tip recording a solo remix that is leaked to radio, only to be pulled because, according to a label source, contracts forbade altering the song in any way. At this point, Monica has “had about enough” and decides to name her whole damn album The Boy Is Mine.

The actual tune in the middle of all this drama creeps up on you with a harp sound that’s like light twinkling on a reflective pool. You don’t groove to it so much as you vibe in it, as Brandy and Monica kick a rather standard script about some tired two-timin’ man (only in the video do they join forces and trap his no-account butt) in their surprisingly complementary styles. Brandy is to groove what Monica is to rhythm. Where Brandy rides the contour of a melody like a wave, Monica advances and recedes, spontaneously creating then dismissing parallel rhythms. She sings like her fellow ATLiens dance, bouncin’ to everything from a Lil’ Jon bass mix to a quiet-storm slow jam.

To slam the song’s lack of passion is to miss the point. Brandy and Monica aren’t spilling their guts to each other–they’re staring each other down. They’ve been relative equals as recording artists. What Brandy has gained in mainstream clout through good-girl roles like Moesha and Cinderella, she’s lost in keep-it-real credibility. While Brandy and Monica have both enjoyed multiplatinum debuts, hit soundtrack songs, and r&b No. 1’s, neither has ever had a pop No. 1. So their collaboration only heats up their battle over who can parlay “Boy” into the most successful sophomore project.

Brandy struck first with a spotty collection that was entrusted to Rodney Jerkins, the r&b prodigy behind the enduring title track to Mary J. Blige’s Share My World, only after giant lizards, buppie flicks, and Lilith ladies kept Puffy, Babyface, and Missy off the project. Like Brandy, Jerkins–a likable kid who’s even mounted his own kinda charming Web site, though (for the record) he doesn’t return e-mail–isn’t yet 20, making Never Say Never almost an r&b youthquake. Tracks like the electrohop “U Don’t Know Me (Like U Used To)” and the Timba-esque title tune are a pleasing marriage of Jerkins’s buoyant beats and the dreamy croons of a singer who has already broken with teen convention by mastering a sort of dusky melancholy–a mood that marks the standout “Almost Doesn’t Count.” The sole misstep in this teen tango is the new single, “Sittin’ on Top of the World,” a “woe is me, I’m successful” duet with Mase that screams–or moans– sophomore slump.

Without Jerkins at the helm, though, Brandy drowns in her own ennui, as is obvious after the album is turned over to Hacks R Us like David Foster, who produced the leaden cover of Bryan Adams’s “Everything I Do (I Do It For You)” and the saccharine Dianne Warren ballad “Have You Ever.” A Warren ballad is like an insurance bond in country and r&b these days–Trisha got one, LeAnn got one, X-Scape got one, Brian McKnight got one, and Monica even got two. But where Brandy drowns in Warren’s sap, Monica keeps her head up–just as Dionne Warwick did with Bacharach-David, and just as she herself did with Warren’s “For You I Will” on Space Jam. When Monica sings “I will go and bring you the moon,” she takes off; when Brandy sings “I will pull a star out of the sky for you,” she’s lost in space.

As Monica’s sophomore set makes clear, this advantage in emotional maturity is her reward for not being scared of her sexuality. We know exactly what she means by “his love is all in me,” and she doesn’t obsess about letting her “secret” go like Aaliyah on her slightly paranoid new smash “Are You That Somebody.” She romances soldiers like her 4-ever Tru boo C-Murder. And her Jermaine Dupri­-produced single “The First Night” is a lesson from the field. When she growls “I wanna get down but not the first night,” she’s not being coy or precious, just wise to the game. And in the midst of the Brandy thing, she’s startin’ mo’ shit by covering Dorothy Moore’s “Misty Blue,” which Mary J. Blige rips on her revelatory new The Tour.

Like “Misty Blue,” the bulk of the album is produced by Dallas Austin, who Monica calls her “play-father.” Austin builds a song by adding sudden hornblasts, scratches, and other bursts of sound to a simple rhythm track. From Deborah Cox’s “Sentimental” to Aretha Franklin’s “I’ll Dip,” he’s called attention to himself by calling attention to the artist, making every vocal seem subtle, reflective, and inspired. Austin and Monica have already created two masterworks: her debut single “Don’t Take It Personal” and (lost on Austin’s flop Fled soundtrack) “Missing You.” Here they rack up two more with the scratchy-funk “Ring Da Bell” and the plaintive “Take Him Back.” (Though if Austin is really Monica’s daddy, he should respect her concepts at the bank by cutting her a slice of that lucrative publishing cheese.) Some credit should also go to co­executive producer Clive Davis, who does know how to mastermind a hit album. Front-loaded with “The Boy Is Mine,” “The First Night,” and the aforementioned Space Jam jam, the album has legs as fine as the ones Monica shows off in that slit-to-the-crotch black skirt she wears in the “Boy” video.

There’s still a part of me that’s gotta love Brandy–the Brandy who appeared on a recent TV Guide cover, sans makeup, braids pulled back, smiling shyly for fear of acting “too fast” or “too grown.” But the ass-splittin’ truth is that Brandy’s a star because she was made one, while Monica would be a star wherever she was. If she was a grocery check-out girl, you’d stand in her line.

Ultimately, Brandy vs. Monica breaks down to our times-defining r&b vs. hip hop debate. Brandy is straight-up r&b teen dream–too peaches-and-cream to be Next’s butta love, but just right for Usher’s nice-and-slow. Monica, on the other hand, is hip hop all the way. Where Brandy thinks she’s being cool with her “slow down Mase you’re killing ’em,” Monica riffs off on “Charge It 2 Da Game,” the latest from her No Limit soldier-in-law Silkk the Shocker. She’s the independent yet “down for her nigga” girl that hip hop has taught us to love. If I was 17, I’d want her as the Mary to my Meth. This boy is hers.