Firstly, Seatguru is completely outdated, antiquated, and incorrect. There are no seats with the 46" legroom it describes.

On LHR-DXB, you have the choice between the fully flat bed on the A380 and the lie flat on the 777. If you're after privacy, sleeping comfort or time at the bar, take the former, and if you're after better service and a little more seat width, take the latter. I find EK's lie flats quite good for sleeping - can't say the same for SQ or QR.

Oh DXB-DAC, take the 777 as far as possible. Even the old seats are better than the 332. I would take whatever LHR connection that allowed me to get on the 777 to DAC. 5+ hours on a 332 is not fun.