The consensus seems to be that generally the A350 offers a better customer experience, despite specific customer fit-outs. Note JAL have 2-4-2 in economy which is one less seat than other 787 operators and they are receiving plaudits for it. However some objectivity is required as judging the 787...

Have flown both the A350 and 787 in both biz & premium and feel the A350 is superior comfort wise (legroom, headroom, noise) and lacks the gimmicky 787 windows, but frankly the difference is marginal and both are excellent aircraft.