Which RPG features the best writing?
In certain circles, I'm hearing Blades in the Dark for this...but it's the new hotness, so that's to be expected. A couple of years ago, I'm sure everyone would have said Apocalypse World because it was oh so edgy with its over-use of expletives.
In other circles, I'm hearing Blue Medusa, Lamentations of the Flame Princess, or anything by that edgy crowd of OSR personalities who values shock factor over elegance of writing or game mechanisms...and who apparently scream down anyone who compares their work to the Emperor's New Clothes.
These are certainly all games that speak to a specific audience, often an audience of fanatical gamer cultists on one side or the other of the mysterious tribalist division between story-games and the OSR.
In my mind, the best RG writing goes back to the work that first exposed me to Jeremy Keller, Chronica Feudalis.
This game is written in the form of an artefact, dug up from the archives of 12th Century monks. It's the kind of technique I first remember seeing in Castle Falkenstein, and while I believe that game did it well, Chronica Feudalis takes it to the next level.