In turbulence, the natural movement of an aircraft is to go nose down in an updraft, and nose down in a downdraft. This is because the airstream vector moves down and up, producing more or less lift. The aircraft then rotates about the nose. The same applies in the vertical axis. It is complicated by the reaction of the pilot, autopilot or yaw damper to the gust, and also the inherent stability of the aircraft, which in turn is dependent on the position of the Centre of Gravity.
I would say then that the smoothest ride is at the front. It is also why it is difficult to tell exactly how bumpy it is in the back from the Flight Deck.