The most useful would be books. Certainly stone tablets would be more durable but less portable and unless you want to jot down some one line commandments the whole thing becomes unwieldy.
For a time after the apocalypse most of our knowledge will be unimportant. History, art and all but the most basic science will be frivolous luxuries. Keep the species history locked away somewhere dark and dry for when it can be useful again. Until then knowledge sharing will likely become more a cultural affair, passing from person to person like some of the societies in the world without books and electricity already do.
It would be fascinating to watch the way knowledge would likely be twisted into stories, then legends as we create our own parables for a new world.