A few years ago my parents flew from Los Angeles to Australia. The flight took over 15 hours! They were very happy that they took the time to find the seat Airplane that would suit them best over the length of the flight.
If you book your flight online, you may be able to choose your seats at the same time. While there are no guarantees that you will actually get the seat you choose, airlines can and do make changes to aircraft and seating charts, spending a little time doing some research may result in a more comfortable flight.
While there probably is no one best seat, there are plenty of seats you want to avoid. I have yet to find anyone that wants the middle seat on an airplane, unless they get the row to themselves! So the choice is between the window and aisle seats. The window seat gives you a great view, and a place to rest your head, but when you want to leave your seat your are going to have to ask at least two other people to move. With the aisle seat you can easily move in and out of your seat. This makes it a good choice if you are like me and need to get up and stretch frequently during a flight. But being seated on the aisle means you will be frequently bumped by your fellow passengers, and the crew.
Other seats that should probably be avoided are the ones directly across from the lavatory. Not only do you get to deal with unpleasant smells, you might find yourself crowded by passengers waiting to use the facilities, and the light going on and off can make sleeping difficult. The lavatory also tends to be noisy. On a long flight the constant flushing sounds can be enough to drive you crazy!
Once you have a general idea of where you want to sit, you can consult with an online source to find more about specific seats on specific aircraft. For instance, if you consult with SeatGuru.com you will find that on the Boeing 737s flown by Continental your probably don’t want any seat on row 10. Those seats don’t recline due to the exit row behind them.
So while you are taking the time to plan your trip, make sure to spend a little time planning your airline seat. It can make a big difference in how enjoyable your flight is.