Book the seats you want, and pray for the best. My + 1 and I are window/aisle travelers and that's what we book. We do not swap with middle seat traveler in order to be together, we travel and pick our seats based on comfort and preference, always aisle and window. Back in the days where you didn't have to pay for seat assignments, most of the time we used to end up with an empty middle seat, since no one wants to sit in the middle. What I do find strange is when choosing seats, you find that the middle seat is already taken, but the window/aisle is open, odd I guess.