In relation to the 777 window seat at least you do have enough room to get past the person next to you in a flat bed position. The cabin crew also have enough room to stand in front of an aisle seated passenger when serving a customer in a window seat. 340, 330-200/300 is a bit more difficult and does present a problem when trying to get past an aisle seat passenger. I personally prefer a window seat in row 2 or 3. I would not choose row 4, because a window is missing. 5,6.7 is normally for families with children and you also keep getting economy passengers sneaking past the curtain to use the toilet so would not picked those seats either. Some of the new 777's now have 4 rows instead of 7 so you need to pick the front seats otherwise you may be split up if Qatar decide to use a 24 passenger business class aircraft instead of a 42 business class aircraft. Video may also help.
http://www.youtube.com/watch?v=O1Ohgd3zopghttp://www.youtube.com/watch?v=Tk9ysBywGvI