Murs by a country mile.
Eminem would've made it big either way, he was already doing his thing before he met Dre, Dre just helped give him his break. He may not have been as big as he ended up being today, but he would've made it eventually. A white MC with that much talent, there is no denying it really. Still love watching Eminem get murked by Juice in a battle, Em had nothing.
You cant say Dre > Eminem though, as a producer, yes, easily, no doubt about it, from a rapper perspective, Eminem shits all over Dre in every way possible, its not even a question, Em > Dre. As mentioned earlier, Dre doesnt even write his own lyrics, Eminem and Hittman writes/wrote alot of the newer stuff and Ren and Ice Cube did most of his N.W.A stuff if I recall correctly (I may be wrong). Same went for Eazy, although he was never a talented MC anyway.
Anyway... new rappers...
O.C vs. A.G