I would have to say Dmitri as I found him the most human of the brothers. I thought that Alexey and Ivan were more like black and white representations of the believer and the atheist that Dostoevsky wanted to use to display his ideas on the consequences of the decline of religion. That's not to say I didn't believe in them as characters, just that Dmitri, with his obvious failings, flaws and passions spoke to me more strongly.