omg, I thought Prince was fantastic...yeah, I agree about how 'all along the watchtower...' alone was worth the admission price, as it were...
I love looking at the tape of the U2 superbowl gig, but I never saw it live and so missed some of its impact as performance. Still, they were so necessarily different in context. The 2002 Superbowl almost didn't happen because of 9/11, we were a nation in deep mourning still and wondering indeed if the Superbowl itself was safe from attack.
The emotional impact of U2's performance was huge. It might have felt less spontaneous, but there's no way it couldn't have and still achieved what it did, what it needed to, as spectacle and statement.
I thought Prince actually made use of some aspects of U2's performance feel in his...
and surely his apparent spontaneity was really very carefully rehearsed of course.
He just gave a kick-ass performance, and did it in incredibly challenging conditions and really just so confidently took that stadium over.
I also just loved it that he included stuff like 'watchtower' and 'proud mary' and such.
It was a great identity-politics moment in its way. Prince messes with that, androgynous and african-american and unapologetic...
and this was a superbowl where finally finally african-american coaches got to play, got to get past identity-politics barriers and play.
I thought it was just great, and tasteful, and the danger factor and the wet factor altogether
cheers!
edit: but since you asked for a real choice, I'd still go with U2!
It was more beautiful and technically pleasing, despite some highlight moments from Prince (I agree a lot of his vocals were hard to hear or weird). U2's show almost belongs in a special category because it was so much more than merely a superbowl halftime show given the circumstances.
Still, Prince beat the pants off all the shows since U2!