I see the thread has evolved. More poll choices, and others weighing in with their opinions on what should "really" be the best.
I voted Doggystyle, but had it been included, Biggie's "Ready to Die", to me was far and away the best rap album ever.
I would also take most of Tupac's albums ahead of any on the list, as well as Biggie's "Life After Death".
Also, most all (but not necessarily all) of the albums from any of Jay-Z, Nas, Ice Cube, Wu-Tang, NWA, West Side Connection, Mack 10, Method Man's solo albums (as well as the ones with Redman), Outkast, Busta Rhymes, and I'm sure I'm forgetting others, would be ahead of all of Eminem's stuff except for maybe Eminem's 2nd album. Don't get me wrong, I love Eminem's early stuff, but, many of the 90's rappers were just so much better.