I think right now, the Eagles are our biggest rivalry, but all-time I'd say the Cowboys are (the Eagles were bad for a really, really long time before Reid and McNabb).
Outside of the division, the 49ers are probably number one all-time, then I'd say Chicago. In recent years Green Bay has been up there, but I wouldn't put them in the top five. I think a lot of Giants fans respect and appreciate a team like Green Bay.