2, 1, 3, 4

others not overly important.

2, 1, 4, 6

Most of my segments are in Y, so extra leg room is a premium for me.

Very much dependant on which aircraft type I'm flying, but general rules are:

1. No middle seat
2. Exit row
1. Window preferred over aisle
7. Having seat in front to be able to stow feet there
4. Neighboring seat currently unoccupied
9. Access to full-size overhead bin (i.e. not sitting under the wings in a BAe146/Avro RJ85/Avro RJ100).

The rest is not important to me.

2
4
6
1
3
5
7
8

Mine are in this order:

1) Window/Aisle preference
4) Neighboring seat currently unoccupied
6) Seat able to recline
3) Close to the front of the plane

My pet peeve is not being able to recline the seat just a little. Usually the exit rows do this, and since I'm short I do not mind the regular seats. I also do not like funky smells. Although usually people don't funk up the lav, there have been a few unfortunate trips for me, so the next would be:
5) Distance from the lav
2) Extra leg room (such as an exit row)

Not even on the radar for me are:
7) Having a seat in front of you for underseat storage
8) Engine noise

1 for me!aisle seats all the way.

Aisle seat
 

From now on I will book an aisle seat in the centre block of 4 seats when travelling long haul. I recently flew Emirates from Dubai to Melbourne (roughly 16 - 18 hours non stop) and was told that the plane wasn't very full. They weren't kidding, I had the whole row to myself and could sleep very comfortably - while watching the person who chose the window seat try to stretch out in 2 seats!

The side 3 seats on a 3-4-3 747 work very nicely for me - I've gotten that a couple of times on the JAL NRT-BKK route, and once pretty recently on CX from HKG-SFO. The new CX seats were especially nice to spread out across as the armrests intrude less and the "recline" increases the seat depth.

WINDOW
 

Window seat as far forward as possible..!A being the ideal.

As far forward in any class.

In forward cabin of business class, if 2 cabins.

There are no perfect seats--except perhaps 1A...

Plus...you can select the perfect seat and sit down and suddenly a woman with a young child appears and with no toys, no baby food, no books, no blanket.
Nightmare-ville.

Perfection is hard to achieve. The best to achieve: a window seat to be out of the noise and bustle. Control of shade. Also more room.
Then, you can control the noise with earplugs, control your comfort in any class with a travel blanket and a pillow, good reading, some light snacks, a zen attitude.
Happy trails.

As most of my travel is in Y on intra-European flights my preference is (in this order):

1) Extra leg room

2) Neighboring seat currently unoccupied

3) Window seat

4) Close to the front of the plane

5) Distance from the lav

Everything else I don't care about.

Window seat - if i get sick, then looking into the horizon helps. Looking at something inside the plane will just make it worse.

Engine noise - I have only flown a few times (on a 737) and the last time I did, I was sitting at the very front of economy class and the engine noise was very loud. I barely heard anything the captain or stewardess said. It was two flights on the same day with different company planes (CSA and JAT), and it was like that on both flights. So I prefer somewhere in the back.

If possible I like to have the whole row (well, half of it, 3 seats) to myself.

My preferences are in this order : aisle seat, seat next to me not occupied,
extra leg room. Don't care if it is in the front,back or middle of the plane.

Usually, aisle > window > middle on longer flights.

Among aisle seats, the fewer people "trapped in" by me sitting in the aisle seat, the better. Window seats that are not "trapped in" are also at the top of the desirability list; those "trapped in" by one other seat are better than those "trapped in" by two other seats. Basically, on longer flights, I like to get up and move around every so often, and do not want to have to disturb others; I also want to be disturbed least by others who want to get up and move around.

Also, avoid non-recline or otherwise undesirable seats.

Being nearer to the exit (particularly when making a connection) is desirable.

1) Aisle only!
4) Neighboring seat currently unoccupied
7) Having a seat in front of you for underseat storage
3) Close to the front of the plane

Extra leg room isn't a big deal for me since I'm barely over 5 feet tall anyway :p

6,2,4,3,1,7,8,5