Michael Jackson is considered to be more iconic. Both Michael Jackson and Prince used to have their own unique styles, and their own persona which separated them from the rest of the lot. After all, this is exactly what the reason of their widespread popularity became. Both having contributed a lot to the global entertainment industry, cannot really be differentiated from each other.
Nevertheless, Michael Jackson had broken all records by selling huge copies of catchy music and by introducing an all new style of dance. Together, these two factors make him slightly more iconic. Even though, both carry their own importance in the entertainment world.