When I fly with my wife we reserve far back of the plane aisle and window with no one in the middle. Every once in a while we luck out with an empty seat between, but more often we end up offering the middle person their choice of aisle or window so we can sit together. We've only been denied once in about 30 flights together. SEA-EWR in July 2014, I remember because it's so strange that someone wanted to sit between a husband and wife for 5 hours in a middle seat.