I was a 747 Captain for 15 years and have maybe something over 10,000 hrs in the left seat of one and got to fly every production model (including the Dash-8/Intercontinental and Dreamlifter) except an SP. A truly brilliant airframe, though the progression of models incorporated refinements. Engines, it's engines that really determine the commercial success of an airplane, that and the wing.
My daughter is a glacier pilot on Denali and now flies the Garret powered Turbine Otter, rather amazing what that power plant has done to the utility of that airframe.
Engines!