In terms of overall lyrical ability, skill and career achievement, my favorite is Ice Cube (his NWA stuff, his earlier solo material and his Westside Connection shit, all of which is classic)...but in terms of staying true to the street game overall, the winner would be Eazy-E...all of Eazy's CDs, like them or not, are Gangsta to the fullest, whereas Cube had a few detours into territory that, to me, just wasn't his forte (I'm thinking mostly of the dance-oriented shit like "We Be Clubbin'", "You Can Do It," "Can U Bounce?" and shit like that).
PEACE!