A couple of people have done them in the past, but I don’t think anyone is recording one right now.

https://youtu.be/DZZNMuJaBc0

A350 in 3-4-3 is hell - worse than a 9ab A330. That's why only low cost airlines have chosen it. I can see the merit for them but for a full-service or even decently-branded airline it's a no-go. 

British Airways has its A350s with 3-4-3, and from personal experience it's not too bad (however I'm the size of a stick insect so I'm probably not one to judge). Definitely wouldn't class BA as being decently-branded anymore though.

I'd pick the A350. Per seat, it burns less fuel than the 787 and supports 3-4-3 config in Economy.

 

FrenchBee (a tiny French long-haul LCC, used to be called FrenchBlue before JetBlue had a hissy fit) has an all-A350 fleet, and I'm pretty sure is currently the most efficient long-haul airline, and seems to be profitable unlike its Norwegian rival.

 

Hainan/Hong Kong Air seem to have tons of A350-900s sitting around which they're trying to get rid of, I'd take advantage of the extremely low lease rates being offered currently and put them to good use.

Aurigny (still going, flew on several of their Britten Norman Trislanders which I also doubt anyone on here has flown, they’re pretty crap in game but absolutely amazing irl)
Blue Islands (apparently on the brink)
British European (became Flybe which is now defunct)
BMI Baby (defunct)

Avro RJs seem underrated in game. Using them as a DC-9-10/20 replacement and found them to be far more profitable.