I find the A350 to be better both for Day and Night flights. More room around your chair and you feel much less tight. On the 787 there is literally nowhere to put anything - barely a spot to rest your phone.

The ONE exception would be if you have a problem with footwells when sleeping. The A350 has a footwell that your feet have to go into...on the 787, they are free in the air. If that's a major issue for you, then 787 is the answer...for me, that doesn't bother me