Yes, as Adrian said it is not possible to say that neither in English nor in French, but you can say: le livre que je préfère, or mon live préféré/ Mon meilleur ami ou un de mes meilleurs amis

It's not really possible to say, even in English "my better book", or "my better friend". You might say 'He is a better friend than you' in a reproach to someone else who is also a friend. You could try ' mon ami préféré' , mon livre préféré