Any notion that U2 is somehow 'better' because they somehow 'stood on their own' without dancers and a marching band is ludicrous, and matter of taste at bare minimum.
U2's 'support' is it's crowd, and they were there in full force with glo-sticks in hand. Or was that spontaneous too? They did their show as they would a normal concert, with the same props and everything. The only thing they changed was how they segued those three songs, otherwise it was straight out of the Elevation tour (ETA: in theory/content, yes I do realize the execution was slightly different). Similarly, Prince has always had something extravagant up his sleeve, it's his style, and he played it to the hilt, just as U2 did.
U2's show was awesome for it's timeliness and tribute, and gets more of an edge from me on the emotional factor as their statement was more powerful than Prince's trip down memory lane (I mean, if you're old like me no way you can't hear him do Purple Rain 20+ years later and not get a bit sentimental, so that's a huge win for U2) and Prince's was awesome for sheer rock-outability, and evens out the score in terms of the fact that I do not believe he was using backing tracks, as evidenced by the more rough transitions, whereas I do believe U2 was.
Face it, in terms of Super Bowl performances, U2 = Prince = U2. It's an even tie.
ETA: holy thread resurrection batman!