My wife and I have flown in the UD a number of times to Asia and we both love it. (But we always fly together and we don't mind climbing over each other.) I find it particularly easy to sleep up there. Even the FAs seem happier up top (maybe less stressed?).

That said, depending on your schedule (how important is it that you be at BKK when you plan to be?), your connection time at ORD, and time of year, given UA's lack of reliability, I might choose the 777.