There is no such thing as a favourite book

OK here is a challenge for you. I believe that it is impossible for a writer to have a favourite book. Having a favourite book means a) you have not read that many books and b) you have not changed over time. Both fatal flaws in writers.
I have literally (sic) thousands of books in my house, nearly all of which I have read, and which I am keeping because I think I might want to read them again. Then there are many, many books which I have read and not kept because I did not like them, more still which were lent to me or borrowed from the library. How could I choose just one of these and say it is my favourite? My favourite is probably the last one I read and enjoyed. My favourites from 10 years ago are completely different to those I enjoy now.
In my teens and 20s I was addicted to SciFi and to a lesser extent, fantasy. I picked up a Robert Heinlein the other day and had to put it down - it was so dated! I read every Doris Lessing and Fay Weldon going in the 1980s - don't really like their more recent stuff.
So I have not listed favourite books on my profile; my favourites are fluid. The best reads I have read in the last few months are: Time Traveller's Wife, The Vanishing Act of Esme Lennox - Maggie O'Farrell (incidentally I left her off yesterday's post, she is an Edinburgh writer too), Human Traces - Sebastian Faulkes. Can I also have Maggie O'Farrell's After You'd Gone even though I read it more than a year ago?
Hey if you are into lists of books then don't miss Nick Hornby's the Polysyllabic Spree - a list of all the books he has bought in the last year. A great read if like me you are depressed by the number of books left in the world that you have not yet read, and the number of days left to you in which to read them.
Please don't recommend any books to me (unless they are exactly like the ones above and therefore you are sure I will love them) simply becuase it will make my list of books I must read before I die much longer and more impossible than it is now.