I wouldn't concider any of those the best groups, or even average. I mean, you only looking at mainstream artists, but even so their are still better groups that have been and that still are.

Best groups are:
The Firm (Foxy Brown, Nas, AZ)
Souls of Mischief (Opio, Tasai, Plan A)
Atmosphere (Slug, Ant)
Deep Puddle Dynamics (Slug, Alias, Sole, Dose-One)
Lightheaded (Ohmega Whatts, Braille, Othello)
Grayskul (???)
People Under the Stairs (???)

I mean, there's tons, but none of the groups you listed are really anymore than a product... As for being a group of artists? Uuuuum, no.