Are you right handed or left handed?

Seriously.

As a right handed person, I've found that while I might prefer the J exit/bulkhead aisle seat on either the 772HD or 773, if the person next to me in the K middle seat is large, I end up tilting left or crouching forward for much of the flight because I want to move my right arm.

If you like to sleep/nap leaning to your right, the L seats will work fine when you lean against the fuselage wall. However, the slide compartment in front of 39L may both limit you extending your legs forward and the seat may be a little cold from air leaks around the door.

19L will require you to climb out past 19K and 19J in order to walk the plane, etc.

The benefits of 19G is you'll have your right arm free. However, leaning left or right in 19G, 19J or 39J into the aisle, you'll likely have people encounters with whomever walk past.

The benefits of 39J and 39L is that you can quickly step forward and take over the lavatory, lock the door and then cry if you need to.

Good luck and let us know what seat you picked and how it worked for those 14 hours!

David