The one you always give as a gift.
This one is more difficult as I don’t actually give the same book over and over again. Actually, I don’t think I have ever given the same book to more than one person.
I mostly give people books that they would want to read, rather than book I think they should read. I’d rather recommend them books that I like and let them make a decision about whether they want to read it.
That said, I do often go into bookshops and grab books of shelves and try and force people into reading them!