Good seats / Bad seats
On most airplanes there are a few seats that are particularly good and particularly bad. The good seats typically have extra legroom (e.g. exit rows); the bad seats typically have less legroom, are directly adjacent to a bathroom (where you have lots of people standing around and the occasional bad smell), or do not lean back fully or at all. Every airplane is different and even the same airplane design at different companies can have slightly different layouts, particularly for larger international flights (e.g. the coach section of a Boeing 777 can have two-seats|aisle|five-seats|aisle|two-seats OR it can have three-seats|aisle|three-seats|aisle|three-seats).
Most airlines provide the seat layouts for their airplanes, but it can be difficult to determine good seats and bad seats from these layouts alone. The best place to find the good seats and bad seats on your next flight is SeatGuru. SeatGuru has a vast and growing collection of the interior layouts for different airlines. For each plane, they provide a graphic seat map where the good seats are green and the poor seats are red. The good seats for most flights can be a little hard to get since many of them (e.g. exit rows) can only be assigned at check-in. However, SeatGuru can definitely help you avoid sitting on a five-hour flight with a seat that doesn't lean back.
General airplane cabin attributes Beyond the individual seats, each region of the airplane interior (i.e. front, middle, back) has particular features that can help you decide, which seat to choose. Getting off the plane fastest
Most people optimize their seat selection to get them off the plane fastest. The closer you are to the front of the plan the faster you'll get off when the plane lands. Largely because of this, airplane seats tend to fill up from front-to-back. However if you check your luggage on a domestic flight, there's really no reason to sit where you'll get of the airplane fastest, because even if you sit at the very rear of the plane and get off last, you'll still likely arrive at the checked luggage belt before your luggage. Only on international flights where you have to wait in line at immigration does your luggage often beat you to the luggage belt. On these international flights, there can often be a strong advantage to seating towards the front of the airplane, because immigration lines can be very slow; by getting out of your plane earlier you'll at least be in line in front of the other 200 people on your flight.
The quietest part of the cabin
The engines of commercial airplanes are most often located under the wings or (less commonly) on the rear fuselage towards the tail. It is noticeably quieter on domestic flights if you sit in front of the wings, which is another reason why people like to sit close to the front. Sitting in front of the wings is rarely possible when you fly coach on international flights as the entire coach section typically starts at the wings – only business and first class seats are in front of the wings.
On international flights, infants are typically placed in the first row of the coach section where beds are often provided that hang on the wall. If screaming kids bother you on airplanes, steer clear of the front of coach on international flights. On the other hand if you have a kid that makes a lot of noise, you'll blend in better and they might find more friends if you sit at the front of coach. On domestic flights, folks with small children often sit towards the back where there is more engine noise to mask any potential child screams. In addition the rear of the cabin is typically close to the bathroom for quick-and-easy diaper changes.
The part of the cabin that fills up last
The rear of an airplane is often the least crowded, which is biggest advantage of sitting in the back. If you sit on the back of the plane, you'll have to wait an extra 10-20 minutes to get off the plane; but unless the plane is full, you'll find more space in the back. In the back, you're much more likely to find a completely empty row, which you can claim as your own for a very spacious and comfortable flight.
Some couples are more proactive about securing more space on a flight and purposely try to get a 3-seat row for two people using the skip-a-middle trick. Most domestic (and may international) airplanes have seats in threes with a row seat, an aisle seat, and a dreaded middle seat. So dreaded are the uncomfortable middle seats that they almost always fill up last. Since planes typically fill up from front-to-back, the middle seats in the back of the airplane are the very last seats to get picked. If you travel with a companion on an airline that allows you to select your seats yourself, you can sometimes secure an entire row by selecting an aisle and a window seat (skipping the middle seat) towards the rear of the aircraft.
There is some risk to this strategy, because if the plane is completely or almost completely full, someone will likely have the middle-seat between you and your companion. When this happens you are still in a fairly good position bargaining-wise, because again no one likes the middle seat. You can typically offer to trade the middle seat person either the window or the aisle. If the person really wants their middle seat however, you're pretty stuck. Rather than spreading out over three seats with your companion, you've got some stranger in between you – that's the potential downside of the skip-a-seat trick.
The complete article here: http://travel.izzid.com/2008/Mar/how_to_choose_airplane_seat/