You have to remember that flights land and approach differently. Take STL for example, sometimes flying there from BDL we fly right next to the Arch and it is an amazing view from the left side, other times we fly in over St. Charles, MO and there is no view of anything. So it all depends. The best bet for DCA would be the left side, however there is no guarantee that you will see anything but some rooftops of homes in Arlington.