My opinion on my favourite characters change all the time. At the time my favourite is Envy from FMA.
He's really evil and ruthless, but weak and sad on the inside. Envy's final scene had me tearing up, which is strange since he is supposed to be a villain. Out of all the characters from FMA, Envy is by far my favourite. And since FMA is on my mind a lot recently, that makes him my favourite overall.