I agree with all of the suggestions mentioned. But why are we all choosing stuff from the year 2000 and higher?
Best drama series? How about Little House on the Prairie? Yeah yeah. I know, I've got to have a screw loose right. But more people tuned to in to this show than anything else anyone has listed. And these shows taught values to the typical household watching them, whereas today's shows are more about observation of sociopathic characters. Those of you not afraid to stick your balls on the line might agree with me on this pick.
As much as I enjoyed the first season of DeadWood, does it really deserve to be listed here? It was a great show and had a solid first season, then the show tanked and went to pot. If you don't believe me, ask yourself why it's off the air?
How about Carnivale? There was a very interesting HBO show that had a solid niche fan base, a show that tried to really think outside of the box, and it tanked too. Good quality shows often suffer like bad quality ones.