I just came back from a trip to BKK, and had 21K on one 742 and three 744s. The 744 has a small LCD screen in front of the seats 21A-B-C and H-J-K. Only thing I don't like about this screen is that if watching a movie with darker scenes, the image starts to "blotch out" in dark areas and lose detail, or actually start projecting a negative image. This seems especially so if viewing from an angle such as in the A or K window seats. A problem that would be easily corrected with a brightness and contrast adjusment as on a laptop, but there is none on this screen!

The benefit of row 21 is that the seats are in a quieter section of the aircraft compared to row 51, which is aft of the engines. Also, on the 744 the window seats on row 51 are spaced such that the window divider is just forward of the seat back, at the precise location where you want to put your arm. Thus, you are cramped compared to getting a few extra inches for your arm if the divider were slightly more forward or aft. This is not a problem for 51K on the 742, as there are only two seats there, and the window seat is not butted up against the window, but actually is a few inches away from it. Stay with what you have!