Joss Whedon’s duties on Buffy and Angel decreased over the runs of both shows, although he was always the executive producer and had final say on every script and plotline. Many fans blame Marti Noxon, who was pretty much the main creative force on the last two seasons of Buffy, for the show’s gradual decline in quality (although I still think the worst Buffy episodes are better than 90% of anything else on TV). One thing about Whedon is that while different episodes had different writer credits, he always returned to write and direct any key, landmark episodes on both shows (such as season finales).
He’s publishing them, now, too, through Cafe Press. There are (or will be) 14 books that you can buy, with a 15th free to everyone who buys all 14.
Oh, yeah, I’m buying them all. I just wish the remaining 18 scripts (according to the back of the book, JMS wrote 92 of the 110 series shows) could also be published.
Rod Serling was the primary writer of “The Twilight Zone” for its entire run, though there were numerous other writers, including Richard Matheson and Earl “The Waltons” Hamner.
Terry Nation wrote the first season of Blake’s 7, but his streak was broken at 14 and he wrote a total of 20 episodes of the 52. Script editor Chris Boucher wrote 9 episodes
Jay Sommers created and cowrote the first 31 episodes of Green Acres, usually with Dick Chevillat. Of the show’s 170 episodes, Sommers and Chevillat were credited (either together or with others) as writers in all but 6. I didn’t count, but it looks like Sommers was credited with well over 100 episodes, and probably close to 150. He also stayed with the show until it was cancelled. I’d say that he’s the leading candidate for the most episodes written.