Im gonna have to go with the Wu Tang Clan, there shit is tight and 36 Chambers is a classic in my opinion. Over the years after going through all the troubles they have still managed to put out quality shit, and not to mention all the tight solo albums members from the group have released. I think NWA is close and they helped push rap to another level. Eazy E, Ice Cube, and Dre were fucking tight, but sometimes I think they were credited with too much then they actually did.