I've given a lot of thought to who I consider the greatest rappers of all time. There's a lot of factors to consider if you're having the discussion. Is it just lyrical content and subject matter? Flow? Beat selection? Success and influence?
And on top of all of that is personal preference. It's just going to stand that some people like some artists better than others and can't explain why...not just in rap, but every genre of music.
I wanted to make a few points on some artists:
-Eminem - Probably the most controversial rapper of the past decade. Let's ignore the racial divide since, no, it does not have an immediate affect on talent. As far as I know, no, he doesn't worship satan. Despite being MIA for the past couple years, Eminem has dramatically changed hip-hop. He came into rap being WILDLY different from ANYONE out and his subject matter had EVERYONE talking about him. I personally consider "Eminem Show" to be one of the best hip-hop albums of all time, on every matter listed above.
-André 3000 - It's a shame he hasn't rapped all too much on the last two Outkast albums, because he is a lyrical GENIUS. His flow is impeccable and his production style is extremely unique. His singing ability only makes him that much better, but again, I wish he rapped more. I'm a huge fan of Big Boi as well, but I feel that 3000's the most underrated lyricist alive today.
-Soulja Boy - Terrible lyricist? Yes. Annoying? Yes. Successful? Yes. Think about this. His name appears 11 times on this page alone, a short thread about Eminem on a Pokemon message board. How did he do it? He put his OWN name out there. He's famous because of one person - himself. The one song everyone knows him for, he created himself. Everything - instrumental, lyrics. Then he threw it up in dozens of different forms on YouTube (genius) and got people all over the WORLD talking about it. Search on YouTube and see how many videos using that song you can find. Bet you can't count it on one hand!
-Lil Wayne - It took me a while to decide just what I thought of him. He's obviously successful in a struggling industry, and you can hear him on at least one song by every major artist out. Can't deny his accomplishments. Personally though, it feels like Lil Wayne is like...the Starter Deck of rap. A lot of the metaphors he uses don't make any sense at all (thread on this coming soon), but his flow is nearly flawless, so everything he does say sounds great coming out of his mouth. And kids love to imitate.
Finally, keep this in mind. Rap careers nowadays last about...a year, maybe two (which equates to one, maybe two albums). Any rapper who can keep people talking about them in a music sense must be doing something right.