Which American drama do you like best?

I like One Tree Hill and Castle best, but I also like series like Big Bang.

The Big Bang Theory isn't a drama. It's a sitcom (situational comedy), a genre that is defined by extensive humor, episodic plots, and a confined setting (i.e. the "situation"). Dramas are far more serious in their nature, and they have a focus on season-long storylines. Gossip Girl could be considered a teen drama, but BBT definitely isn't.

With that said, my favorite drama is probably either Breaking Bad or Supernatural.

I don´t know if these are dramas but I like some series like: 90210, doctor house, once upon a time, CSI, America´s next top model, and others !

Shameless US is the best American drama I have ever seen.