In a fight to first KO:
1. Dick Grayson
2. Jason Todd
3. Damien Wayne
4. Tim Drake
In non-lethal combat, I think Dick is a little more practiced than Jason. Jason would have to not use the majority of his skill set in order to compete, putting him at a severe limitation.
In a fight to the death:
1. Jason Todd
2. Damien Wayne
3. Tim Drake
4. Dick Grayson
Jason and Damien are straight up killers. Tim could probably kill if necessary, but I think Dick is too big a softy to ever take a life.