For one thing, the AC ones are SD-70MAC's where the earlier ones like Lake State owns are just SD-70M's. General Electric and Progressive (formerly Electromotive) don't even manufacture any more DC locomotives any more for the American railroad scene, and most of the big 6 major US railroads are rebuilding a lot of their old DC units to AC. The big thing seems to be better starting tractive effort, the traction motors will not overheat when put to the max, allows better fuel economy, and less maintenance all around. As far as spotting features, someone else with more knowledge on this subject needs to chime in. Or you could do a little research.