Just been looking at cabin width of both types of plane, airbus A330 is 17ft 3", the Boeing 787 is 18ft, only 9 inch wider with 9 seats as opposed to 8. Based on those dimensions I think I would choose the Airbus.
When we did fly we did plenty of long haul journeys on A330's and A340's, and never experienced any problems, and TBH the older Boeing 767's of US Air with the 2-3-2 configuration were the most comfortable economy planes we ever flew on, obviously IMO.