I really like the movie thread but I think most folks spend much more time watching a particular TV show, some maybe over and over again. My five:
Frasier - it’s a perfect 20 minute break from things show. Each episode almost self contained, the performance are always great and there’s hardly any dud episodes. And when it’s great it’s among the best TV of all time. I’ve been Netflixing Frasier for about as long as I remember, before that it was DVD’s or VHS. And I didn’t even watch it when it was being broadcast.
Friends - look, I’ve been married for a long time and you watch stuff together. It’s the sacrifice you make.
Gilmore Girls - wifey loves her Gilmore Girls. And I can see why, it’s like Frasier in lots of ways. Stellar cast, perfect brain candy, easy to watch.
Spartacus - there’s two types of people in the world for me - brothers who love Spartacus and other I’ll never truly love no matter how awesome they are. I’ve watched the series 5-6 times now and make a habit of watching it every year. I’m adding Black Sails and Vikings to that same regiment so before too long I’ll never need any more TV.
DS9 - more than any other Trek, it’s been show I’ve been happy to go back to again and again. If I’m flicking channels and I find DS9 I’m pretty happy to just let it run no matter where it is in the episode. I’ve got them all on DVD, and that replaced having them all on VHS. You can tell you love a show if you keep buying it to keep up with technology.