comes down the preference, a 2 way will obviously lock up both on accel and decel so it makes the diff movement very predictable when coming on and off the throttle, hence why its popular for drift, this unfortunately means that coming in, middle and out of the corner the rear wheels arnt going to want turn at different rates on either acceleration or deceleration, this causes some understeer, especially coming into the corner and on the tighter corners. 1.5way allows u to feather off the throttle and open up the diff meaning it can turn in easier, but when u put ur foot back down it locks up again and allows u to get the power down. for me the 1.5way is preferable, but as i said, its about preference.