HBO clearly has had some of the greatest TV shows ever (from Larry Sanders to The Sopranos and all those in between). A lot of that can be attributed to the language, the sexual content and the lesser standards HBO has.
So, what TV shows could have been ever better had they been on HBO?
Bill Simmons (the Sports Guy) went with Skin - - the Fox show of a couple of years ago with Ron Silver and Olivia Wilde, while also mentioning NYPD Blue. One of his readers suggested Lost, another The Man Show.
Personally, I think 24 would have been an even better fit for HBO. The language could have fit better, the killings, etc.