Perfect, completed, greatest TV show of all time, greatest cultural work of the last 30 years, hyperbole really isn't possible with it: The Wire
Perfect but incomplete: Deadwood, Breaking Bad
Near-perfect: The Sopranos
Flawed but absolutely wonderful: Lost, The Shield, BSG, FNL, The West Wing, Mad Men
(Merely) Very Good: Dexter, Six Feet Under
Either great or awful depending on the season: 24 (also Rescue Me)
Breaking Bad belongs on the Wire's tier after their recent season, I think. If the last 16 episodes are really fantastic it could make a case for best show ever made. It would have to blow the previous 4 out of the water, but given that every BB season has been progressively better I think Gilligan et al have it in them. The Wire ended on its weakest season which is something I certainly can't picture BB doing.
Sons of Anarchy and Treme should probably get added to the Very Good tier. Maybe Justified too once I've gotten through both seasons.
EDIT: may have spoken too soon on Sons of Anarchy. The season 4 finale featured maybe the dumbest plot twist I've ever seen in anything, dropped in from out of absolutely fucking nowhere.