a) Questo e` il mio scrittore preferito.
b) Questo scrittore e` stato molto favorito dall'editore.
In (a) you are stating something about your personal tastes, that YOU (the speaker) like best a certain writer, you are not stating an intrinsic property of the writer.
In (b) you are stating a FACT related to the writer, i.e. that he is in a great and special cinsideration by the editor that treats him in a special way.
Essere favoriti: ricevere dei favori.