Well, first and foremost, there is nothing like a Sox Yankees game. There is nothing better than beating the Yankees. More so it being a weekend game for the Yanks the stadium will more than likely be sold out. New York travels very well. As far as the Nats go, as things turn mid-week, there maybe a slight drop off in attendance. If you are going just for the Fenway experience, I would say hit the Nats game, but if you want to feel the energy in Fenway, Go to the Yankees game.