We often go in row 2 if we have under seat sized baggage, so we are not fighting for locker space or worried about when we board. If alone, I often use the space under the middle seat, politely asking the other seat occupant if that seems appropriate. Remember, it's only takeoff and landing that it needs to be under the seat so, even if using the seat in front, you can move it out for better legroom for the majority of the flight.