Both are NOT correct, both are rein effects however. A direct rein of opposition Pulling one rein is a backward action, it will cause the horse to throw the quarters out and (over)bend the neck, and if combined with letting the other loose only pulls the bit through the mouth (unless there is a D/fulmer/fullcheek). IF the student learns to pull back with the reins it is very difficult to overcome/replace. The horse must come to the contact, not the opposite.
When using an opening or leading rein, the rein comes lighty away from the neck (NOT forward), or in a more subtle way by merely turning the thumb over to the outside (ie nails showing/little finger coming closer to the neck). The purpose of such a rein is to direct the horse into the outside connection which then allows for straightness.
That said, the outside rein MUST be kept lightly connected, it does not go forward/release, it functions as the 'receiver' and forms a kind of wall that the flexion inside can move into. Both reins must have the same weight (lightly/ounces).