What is the best Hip-Hop artist of all time ?

There are a variety of Hip-Hop artists that have been spanning through multiple years, hip-hop in the 80s is a lot different than the modern era hip-hop. The genre is constantly evolving and multiple sub-genres has emerged, like Lo-Fi, Trip-hop, Gangsta rap, ignorant rap etc...
It's also hard to measure what makes the success of an artist, is it the records sold ? the number of songs ? the activity of the fanbase ? the quality of the rhymes ? the impact his song had ? What the artist do outside of it's musical activity ? it's longevity ?
For example we can say that Run-DMC has been the first rap group to really push the genre forward as they were the first group to be on Mtv, having a sponsorship with Adidas, and mixing Rock with Rap in their Song with Aerosmith, but their longevity has been shortened due to the murdering of Jam Master Jay.
Tupac or Notorious Big are acknowledged by a lot has the best rappers of all time because of their rhyme scheme and the fact that their song remains classics today.