You can say that something is "better" than something else based in subjetive factors ("because I like it more", and this depend of time, if I just read "Lord of the Rings" and compare it with "Enders Game" that I readed like 10 years ago, well, the feeling of better probably will go to LOTR, in part because my memory, in part because all of this changed me) or objetive factors (i.e. because A is larger/colorful/simmetrical/etc than B, and I define that that comparisions are THE way to compare them) or a combination of both.
The objetive way, in fact, should be expressed like A is better than B in all this ways to compare them. I can't say properly "a plane is better than a car" without using a specific amount of ways for comparing them, being aware of this or not, if I thinking now in that I have to go to England, probably would say that a plane is better than a car, but not because I compared them in every possible way.
Now, "best" is an extension of "better", where you compare against a certain alternatives, but you have clear that saying generic things like "the best book of all times" doesn't mean every book, neither mean every book one have read, but maybe is every book that the one that is defining the list is aware right now.
So, when you read things like "The best books of all times", remember that mean what certain amount of people feels (or remember that feels) about a limited amount of books, and nothing more, so is possible that you don't like them or not agree with the order at least... but it could serve as a guide.