If you have ever travelled on both these routes, you would have observed that N35 goes through much deprived areas of Shangla and Kohistan districts and also passes through a larger area of Diamir as compared to N15 which passes from Mansehra, Kaghan, Naran, Babusar Top and meets N35 at Chilas. Yes, Babusar Top has an altitude of more than 13,000 feet above sea level and has some of the steepest slopes in this area but it does not prevent engineers from coming to a feasible solution weather it be a tunnel or an alternate route around the pass. In my opinion, N35 route is better for a reason that it goes through remote and ignored areas of Pakistan (here i am not using the word KPK for a reason) which can be helpful in economic progress and enhancing lifestyle of people of these areas.