I would run a load of commercially funded taxibuses, because they would be low-cost to run and could potentially benefit passengers if the fastest route between two places involved narrow streets/roads.
Some early ideas:
TB3: Washington, Oxclose, Crowther, Ayton, Team Valley, Newcastle
TB19: Gateshead, Whitehall Road, Bensham Hospital, Team Valley
TB25: Chester-Le-Street, Plawsworth, Kimblesworth, Nettlesworth, Sacriston, Witton Gilbert
TB33: Chester-Le-Street, Hilda Park, Pelton, Perkinsville
TB59: Gateshead, Q.E Hospital, Felling Square, Fewster Square, Ellen Wilkinson Estate, Wardley