It's almost impossible to answer this question for me... We have a loooot of tv shows that are spetacular, but I really enjoy when the writters put a lot of effort to create and realy explore the possibilities of an scenario.
I think Breaking Bad and Better Call Saul are a good example of this effort.
Also, both series put a lot of effort in the character development as well, and that's amazing, they make you simpatize with people that are bad, but are real and deep, wich you are able to see a lot of layers from their persona, and understand that, the life is realy not that simple as we wish.