Guhhh, I really hope it's not Eminem. The main problem with him is that he's SO HATEFUL. His music might be decent, but he's homophobic and misogynistic and he'd screw with my vibes. The main difference between him and acts like Jay-Z or Kanye is that, while Jay-Z and Kanye might not be beacons of morality, they don't rap about hating or wanting to hurt gay people. Eminem is vile and his presence is not desired by me. Also I owned the edited version of The Eminem Show when I was younger and an entire song was omitted. AN ENTIRE SONG.
I know this is an old post, but I can't help point out that Eminem is not homophobic at all. One of his best friends is Elton John. You may remember when Elton and Em performed together at the grammys? I won't disagree that he's misogynistic, but he is certainly not homophobic, just because he says fag a lot.
To offer my two cents to the thread, I would love Eminem to headline, but I'd also love to see Beastie Boys again, so I'm kinda torn.