Setting aside artistic value and focusing solely on enjoyment and "must see'ness" at the time I was watching.
And emphasizing that not all of these have aged well but "at the time"...
Seinfeld (natch)
Firefly (made significantly better since it had a chance to "wrap up" via an excellent movie)
Frasier
Burn Notice (really strong television for a USA Network show)
Buffy
Angel
Star Blazers (I honestly remember virtually nothing about this cartoon except the theme song and that it RULED when I was a kid...space soap opera on a freakin' battleship-space-cruiser)
Modern Family
Dukes of Hazard (again, this was "must watch" TV of my youth...could also have gone with Knight Rider or Magnum PI or The A-Team but this was the one)
Cheers
My problem is there were so many shows that were REALLY GREAT for a few seasons but then tailed off. Which is also why I'm not listing anything on the air today (other than Modern Family) simply because there's no guarantee they don't turn into lousy shows. For instance, I enjoy the present-day super hero shows (Arrow and Flash and Daredevil, etc) but I see vast potential for shark jumpingness in the future (I couldn't even finish the first season of Legends of Tomorrow it got so bad).
True confessions: I've only seen the first four episodes of Breaking Bad (but I will someday watch the rest). I think Sopranos and Game of Thrones are vastly overrated. I really liked How I Met Your Mother and Friends. I've never seen The Wire. As a kid, I could have watched Spider-Man and His Amazing Friends and Challenge of the Super-Friends all day, every day. Anyone else remember Manimal? Remington Steele was awesome. So was Moonlighting (until it wasn't). I still like the theme song to Greatest American Hero. Barbara Eden in I Dream of Jeannie really did it for me. The Fonz was the bomb. Gilligan's Island earns credit as "best show to ever feature the Harlem Globetrotters stranded on a desert island".
End of confessions.