Can't answer your questions specific to Air China, but in terms of the United 747 flight I definitely recommend the upper deck and, if you can get it, row 15 (the exit row). The upper deck is more private than downstairs, is quieter, has better service, and has very handy storage cabinets next to the window seats. Row 15 has by far the most legroom and you don't get anyone reclining back into your space. The only slight disadvantage is that there is no seatback in front of you into which you can stick magazines, etc. But if I understand your post correctly, when you say "we" I assume you mean there are (at least) two of you traveling together, so even if in the aisle seat you can easily access the storage cabinet next to the window for stuff like that.

For a bit more info on this, check out seatguru.com and more specifically the link there that provides a diagram and seat recommendations re the United 747: http://www.seatguru.com/airlines/Uni...ng_747-400.php

You also might want to post your United-specific question under the United Mileage Plus program heading to get more responses and opinions--though I've told you all you need to know.

Hope this helps. And have a great trip!