I can't believe nobody has mentioned Ice Cube.
He never reached sales like Tupac did, but he is definitely one of greatest artists of all time.
1 Tupac
2 Dr Dre (because you are asking for the best "artists" and not rappers specifically)
3 Eazy E
4 Ice Cube
5 1990s Snoop
6-10 in no order Eminem, DMX, Jay-Z, Scarface, Freddie Gibbs ("What it be like" is easily in my top 5 songs of all time)
That's my own personal list.
I'm a huge fan of 90's hip hop and cannot stand the crap that comes out nowadays.
Has anyone ever heard of "Winnipegs Most"?
Just saw them on a news show (maybe the National?) last week and checked them out. Native group from Winnipeg and they are actually pretty amazing.
http://http://www.youtube.com/watch?v=tZXJm9Lprxc