According to several TV writers, bloggers, and cultural critics, each of these is the best show on television.
The Wire
Lost
Friday Night Lights
Deadwood
30 Rock
The Daily Show
Battlestar Galactica
The Sopranos
Arrested Development
Studio 60
South Park
Veronica Mars
Six Feet Under
Hard Knocks: Training Camp with the Dallas Cowboys
The Colbert Report
Mad Men
The West Wing
Mad Men is getting the most buzz lately but The Wire is still the high-water mark (in my opinion as well as the web's collective opinion according to Google). The Sopranos gets surprisingly little love as the top show, although its relatively weak competition back in the early 2000s perhaps means it didn't need to be said. The quality of television for the past 3-5 years is impressive...most of the shows listed above were all on at the same time.