United 744's get pretty uncomfortable after say, 3 hours of flight as it gets a bit cramped. If your flight is over 4 hours long you may want to either get an aisle seat (so you can get up easily and walk around) or try to sit in E+ by politely asking the gate agent if there are any E+ seats left. Oh, there's also the bulkhead.
Its better to be on the ground wishing you were in the air than be in the air wishing you were on the ground. Fly safe!