I think HBO, despite not being at their historical peak by any means, is still king. Boardwark Empire and GoT are both shows where every time an episode ends, I lament having to wait a week. And Newsroom and Girls are great too, although some people don't "get" them. Actually, that's kind of true of BE, too.
Really, HBO has taken some major risks with shows that require the viewer to meet the show halfway and get in the show's mindset. I think for the most part, it's worked.
I even still enjoy True Blood quite a bit, just because I understand that the point of the show for a while now (maybe all along) has been to see how much further they'll push the campiness and ridiculousness. The less seriously you take TB, the better a show it becomes.
Anyway, I like AMC's big 3, but overall, HBO still has them beat in my book. Showtime? Eh... Dexter has become a huge chore to watch, Homeland is okay but never lives up to early season 1. Shameless is pretty good.