I've only flown on Qatar's A350 (in economy) . Never been on a 787.
I enjoyed it. Legroom was decent (I am 6"2) and there was also enough room to be comfortable and not feel squashed by the person next to you. The aircraft was indeed pretty quiet and on the whole felt very pleasant.
787s seem to get a terrible review in general in economy so I am intent on avoiding them if it'll be a Y flight. The A350 is fine with 9 across whilst the 787 is cramped due to not being designed with that in mind, seems to be the consensus. BA's 787s also seem to have those irritating IFE boxes blocking legroom, which will not help. As I said said though, never flown on it so could be doing it an injustice. Feedback does however seem to be scathing