100 percent David Tennant.
He was just perfect, I think. His expressions, looks, clothes, voice, hyperactivity... Everything was completely perfect. I don't think there has been or will ever be a doctor that can beat him, and I just think he was made for that role.
However, I like how every actor brings their own elements into playing the character. I started watching when David Tennant was the doctor, so I went back and watched some older episodes and really liked some of the other doctors too.
However I just don't think Matt Smith is very right for the role. I watched 1 series of him in it as the doctor, and tried to watch the next one but I have sadly stopped watching Doctor Who. I just don't really like the direction it's going in, they changed too much.