My favourite book of all time? A Canticle for Leibowitz.
A Canticle for Leibowitz is also my all time favorite book !!!
By the way, for those who like Fallout, that book also takes place in a post nuclear world as civilization rebuilds itself. It's really funny in parts, and sad and thought provoking in others.
But as far as series go, LOTR is obvious. But aside from that, I like Asimov's
Foundation Series.
I also loved Dune but that is one of my least favorite book series. The first book was fantastic but all the sequels by Frank Herbert were crud. IMO.