if you mean "which book was the best book among the books what you read until now?",

then it will be "지금까지 읽은 책 중에 어떤 것이 최고의 책이었어요?"

지금까지 = untin now

읽은 책 = the books what you read

Noun 중에 = among Noun

최고의 책 = best book

이다(Adjective)/있다(Verb) = am, are, is

이었다(Adjective)/있었다(Verb) = was, were, was

and my best book was the "Ladyhawk"

there is the movie about it too (Michelle Pfeiffer, Matthew Broderick and Rutger Hauer)

it's about sad but beautiful love story and it has happy ending at the end

I hope my correction and opinion about my best book could help you ^___^

저는.. Tolstoy요^^

교훈적인 내용이 많이 들어가 있는 것 같아 좋았어요~!

How about you?

The Thief of Always by Clive Barker.

좋은 이야기 있어요. :)