NS maintains their track better.
At first, I started modelling CSX, but at the club that I belong to, we have a guy that owns more locomotives than CSX ever did, a guy who models BNSF, a guy who models Conrail, another guy who models CSX, two guys that model UP, a guy who also models Conrail, and a guy who models Boston and Maine steam.
Instead of competing with the other two guys for addresses for CSX locomotives (the president literally owns everything they made for CSX, and then some since he also custom paints). I decided to model a local regional line, Pan Am Railways (formerly Guilford Rail System, which is a holding company that operates the Boston and Maine, Maine Central, Portland Terminal, and Springfield Terminal). At the time, Pan Am Railways ran pretty much all GP40s. Then (the prototype) Pan Am Railways partnered with Norfolk Southern to create the Patriot Corridor (which is basically Pan Am's main line that NS is paying to fix up and maintain in return for trackage rights) so I started modeling NS as well since there are rumors going around that NS may buy out Pan Am since they are very interested in getting into the New England area (to compete with CSX)