I would prefer lethal injection over the electric chair because it is not violent at all. A lethal injection simply takes away the life quietly and in peace, and allows the person to go in peace. The electric chair on the other hand is pretty gruesome method of execution.
In my view, the lethal injection is perhaps the most peaceful and better way to die. In case I was a criminal who was sentenced to die, the lethal injection would be the best thing to do. At least however, the electric chair is still not as gruesome as the other medieval methods.