Questions have been asked what the best 'beginner' games are. Good suggestions have been given. Which RPG's, in your experience, have the best Gamemaster advice sections? Both for initial learning of the 'craft', as well as 'masterclass' level?

Which RPG's, in your experience, have good advice for gamemasters in their rulebooks, both for novice and experienced gamemasters?

Please keep in mind that this question is not about good games for beginners. It is about good advice for gamemasters.