A somewhat circular pattern of brushing teeth, I think removes plaque effectively. This is because it picks up the material and sweeps it out. The other methods simply move the material and impact it against other surfaces. It's like dusting. If you dust side to side or up and down, you just push the dust against the walls or floor. But if you use circular motion, you dislodge and remove it.
This is the way young grandmom brushes her teeth. :-)