Oh, and I gave my vote to Jay-Z.
"Best" is such a general term, its hard to determine what the criteria was. Here was what I used:
1)Universal Appeal: are this persons' songs ones that only aficionados can appreciate, or can many people see the artistic value
2) Musicality: Beats, Flow, Instruments (really, most of his success here is due to Kanye though)
3) Content: are the songs meaningful, do they have lasting themes?
4) Lyrical quality: What about metaphors, similes, alliteration, assonance, and allusions?
5) Influence: creation of slang, new styles, is this persons work sampled?
6) Proliferation: is there a meaningful body of work to assess?
Tupac would have had my vote up until sometime soon after the Black Album, but since then its been Jay-Z.
People like Rakim, Mad Skillz, they hit real well on #4, but to me thats not what its all about. Others are all about #3, like Talib and Common, and to me thats very enjoyable, but for others thats isnt a focus when listening, just a side benefit.