So, I've come up with 10 criteria. Each have up to 5 attainable points each (with 5 being the best, and 1 being the worst). They will be added in total and a rapper can earn a maximum of 50 points combined.
This is just a temporary rubric I made in 2 minutes. I could probably find a better one at some point.
* Lyricism (From a technical aspect, the complexity and intricacy of the words written)
* Flow (How the syllables are arranged, syncopated, the speed and tempo, and such)
* Delivery (The voice ,how it conveys the mood of the song, volume, intonation and such)
* Storytelling (How well can they paint an image in the mind, and tell a gripping story?)
* Impact (What was their legacy? Did they influence a lot of great rappers)
* Sales (Self-explanatory. And basically, a popularity contest)
* Innovation (Did they add something new to hiphop or are they simply derived from another act)
* Imagination (Do they use creative concepts in their songwriting? Do they try new things?)
* Message (Are there greater cultural or artistic meanings to their writing? Or is it just words)
* Consistency (Is their greatness displayed in most of their songs or only a few of them)
Lyricism/Flow/Delivery/Storytelling/Impact/Sales/Innovation/Imagination/Message/Consistency
Jay Z
4/5/4/4/5/5/5/4/3/5 = 44/50
Kanye West
3/3/4/4/4/5/4/4/3/4 = 38/50
Lil Wayne
3/3/3/3/5/5/4/3/3/1 = 33/50
50 Cent
3/3/4/4/5/5/3/3/3/2 = 35/50
Dr. Dre
1/3/4/3/5/5/4/2/2/3 = 32/50
Method Man
4/5/5/3/4/4/3/3/3/4 = 38/50
GZA
5/5/3/3/4/4/3/4/3/4 = 38/50
Old Dirty Bastard
2/4/5/3/4/4/5/5/2/3 = 37/50
RZA
5/3/3/2/3/3/4/4/4/3 = 34/50
Raekwon
3/4/4/5/4/4/3/3/5/4 = 39/50
Rakim
3/5/5/4/5/5/5/3/3/2 = 39/50
Tupac Shakur
3/4/5/5/5/5/4/4/5/3 = 43/50
Notorious BIG
3/5/5/5/5/5/3/2/2/4 = 39/50
Eminem
5/5/4/5/5/5/5/5/5/3 = 47/50
Nas
5/5/5/5/5/5/4/4/4/3 = 45/50