Have a few probably and after each really good read I think....'yeh that is one of my favourites now', but can't say I have one particular favourite. Something I read years ago and then maybe try and read now, I would not necessarily like now, as I find my taste in books has changed slightly.
For a long while it was 'The Shell Seekers' - Rosamunde Pilcher. I really enjoyed it first time round, and have probably read it twice since then, so does that count.
Chocolat - Joanne Harris is another firm favourite though.