As most people here will already know, my favorite characters directly result from hearing the actor or actress speak about their character, most importantly, Lindsey and Connor.
I've always been a Lindsey fan, ever since the first season, but it wasn't until I heard Christian speak about how much he loved playing Lindsey and how out of his way he went to avoid Lindsey being killed off did I truly fall in love with that character. The character of Lindsey was created for Chris because Joss loved him when he auditioned for the part of Riley and wanted to keep him around. To know that the creator of the show went out of his way to have someone on his show spoke volumes to me. That, and the fact that Joss allowed Chris to get away with avoiding having Lindsey be killed. When Chris refused to do the episodes where the plan was for Lindsey to die, instead of just killing him off screen and having Angel and the crew find out, Joss allowed him to live. I love that.
It's the same with Connor. Hearing Vincent talk about how much he loved playing Connor, even though he got such a hard time from the fans, was very interesting to me. Vinnie loved playing Connor, he never thought Connor was a bad guy, just confused about who and what he should believe in, and hearing Vinnie talk like that made me realize how misunderstood Connor is.
To a lesser extent, the same thing happened with Clare Kramer and Juliet Landau, and this past weekend with Jared Padalecki.
For me, it ALWAYS depends on what the actor thinks about their character.