David Milch, at his best, was the best.

J Michael Straczynski. He's niche, comics and sci-fi, but I'd argue that Babylon 5 is one of the great achievements of 90s TV.

From the UK, John Sullivan, who wrote Only Fools and Horses, Linehan, Horowitz keeps churning people pleasing tv, year after year. Is it highest quality? Maybe not. But the consistency is impressive.