It is always an exhilarating experience to leave a dance concert eagerly chatting in agreement with those around you about that one favorite piece. Yet it is perhaps the sign of an even stronger concert when those around you are instead in amicable disagreement, each passionately arguing why his or her favorite piece was the “one.” So was the case with Jessica Lang Dance, presented by Celebrity Series of Boston at the Boch Center Shubert Theatre last week.