I would say the 787 is the finest plane when it comes to comfort for biologicals. I say biologicals because even dogs, cats, and horses seem to prefer the 787. I personally feel a slight difference between the 787 and the A350 - I think I feel better in a 787. Although this is not a perfect comparison - as the passengers, route, and airline are not all the same which may contribute to an imperfect objectivity.
So the question becomes... Why doesn't every airline switch to the 787? And why do passengers think the A350 and the 787 are competitor aircraft but the airlines consider the A350 and 777 to be competitive aircraft and consider the 787 a class in its own? Especially when the 787 carries nearly the same amount of passengers as a 777/A350 and is supposedly 20% more fuel efficient.
So I asked an Emirates executive who gave me some basic information. And I realized that I made a lot of assumptions. He told me the following:
1. While it is true the 787 and A350 share many similarities as both are the only two carbon fiber bodied planes, and I can see why passengers assume these two planes are competitive; the A350 is definitely seen as a competitor to the 777 despite the 777 being aluminum bodied.
2. The reason why the 777 is still very favorable for airlines is because its total payload in weight is much higher than a 787. So while a 787 is 20% more fuel efficient from a per passenger seat perspective, that advantage drops dramatically once cargo is factored. Airlines make more money on cargo than passengers sometimes. So the ability to carry cargo is important and valuable.
3. The A350 is slightly larger than the 787 in terms of passenger capacity and has a lot higher total weight payload, meaning it can carry more cargo. The carbon fiber hull of the A350 also contributes to the fuel efficiency as well. So to many airlines, this may be the sweet spot. You've got better fuel efficiency, similar to 777 in passenger seating, and similar to 777 in total weight payload.
4. So then I asked why doesn't every airline just switch to an A350? And the response was much more complex and touched politics, government influences, Airbus' capacity to deliver so many planes, diversification, etc.