To answer the OP's original question it all depends what you define in pop culture as "Superior":
If you are referring to global popularity at their peak, then there is no question MJ during the Thriller era, and then during the Bad album and tour wins hands down as iconically it was at Elvis & Beatle-mania levels whenever he appeared anywhere.
If you are referring to remaining a relevant chart recording artist with a degree of critical acclaim, then there is no question Madonna wins as her albums always reached the upper heights of the chart and did not fall away quickly whilst mining a handful of chart singles up until & including her Confessions On A Dancefloor album which is an incredible run for a recording artist which has arguably not been surpassed without dips in their popularity in between.
If you are referring to artistry/critical acclaim/musicianship, then there is little doubt Prince wins as he spent a very prolific 10/15 years producing a body of work that bore comparison with David Bowie a decade earlier; and even in the last decade he still possesses great musicianship and showmanship as can be evidenced by this 2004 Rock'n'Roll Hall Of Fame performance (from 3min 27 secs onwards
http://www.youtube.com/watch?v=6SFNW5F8K9Y )
If you want my honest answer, I personally prefer Prince (and his body of work/live performances, etc because he was a fantastic musician/songwriter/producer and a not so great popstar), but in terms of a legacy like The Beatles or Elvis he falls short because he lacked the visual icon-ism of MJ & Madonna.
I feel I can't give the prize to MJ because his body of music lacked versatility which is incredibly frustrating as he was clearly an immensely talented performer, but he increasingly (post Quincy Jones) let spectacle overtake substance as best typified by this legendary performance
http://www.youtube.com/watch?v=ttq_xRSCZDE where the first 8.5 minutes show a fantastic great charismatic singer, but then the last 5 minutes show a gimmicky mime artist showman about to go supernova with all the surgery, eccentric behaviour and paranoia that followed which sadly fore shortened his life. Hence he chased popularity to the detriment of his artistry when I believe if he put his mind to it he could have eclipsed Stevie Wonder, Marvin Gaye & Prince in that sense; and I so wish instead of doing spectacular tours where the songs and choreography were timed to the milli-second featuring too much lip-syncing cheating his own talent, he hired a superb set of musicians as Miles Davis, James Brown, Stevie Wonder & Prince did in the past and put on a fantastic basic rawer show as that could have been something truly special instead of some of the nonsense he did on tour.
That leaves us with Madonna, whom I feel ploughed a middle path between Prince's artistry & MJ's hype & showmanship. Madonna came along at the perfect time as MTV was emerging, and whilst she was clearly not as musically talented as the other two artists (although she was a great dancer), she had an ambitious drive and understanding of previous pop culture and visual imagery that they lacked. Madonna was the perfect combination of punk and disco, she quickly learnt to manipulate the media by giving good head(lines), she had the sexuality of Prince, the ability to create a spectacle/moment like MJ, but she surpassed the other two due to her ability to reinvent herself by utilizing Andy Warhol's PopArt concept of "borrowing" things that had been done before (imagery wise: Marilyn Monroe; Bettie Page; Marlene Dietrich; Greta Garbo; Brigitte Bardot; Jayne Mansfield; Debbie Harry, ...) but putting them into a new context; and more importantly musically by changing/upgrading producers/co-writers so she stayed on or one step ahead of the curve, so even the apparent missteps that were Erotica & American Life are now far more highly regarded than they were then. But unlike (one of her idols) David Bowie in the 1970s/early 1980s she avoided becoming a cult artist and had a much higher degree of global mainstream single chart success which she maintained through to the mid 2000s, a near 25 year run of sustained success that no other music artist can claim to have sustained at the consistent prolificness that Madonna achieved. It is only the last two albums which have seen her finally fall into the age old trap of jumping on the bandwagon as it was becoming tired; not uncoincidentally her vocals, lyrics and videos from her last two albums seem similarly to be less inspired as she appears to be settling into a role as a veteran artist where she can guarantee huge tour receipts, and large first week album sales spikes, but major singles chart success and long running charting albums are a thing of the past. If that does not clinch it, then the fact she broke the glass ceiling to become the first ever female popstar to be the biggest popstar in the world is enough for me to reckon in 2062 Madonna will be more highly regarded than her two male rivals.