This issue has some excellent articles on the various aircraft production programs and what is doing well and what is not. It also gives some insight into how some programs like the 737MAX evolved. Boeing favored a clean sheet design but the customers particularly American forced them into the MAX.
Programs doing well include the 737 and A320series. Narrow bodies are in demand. Wide bodies are hurting for sales. A380 is still barely breathing even with Emerites order. The 777x and A330-900 are not strong. 787-900 and A350-900 are the only solid programs. 787 production going to 14 a month. One of largest 330-900 customers may be getting ready to cancel and switch to the A350. Not sure where that leaves us and the program. Airbus still hoping for a large order from a Far East airline to put the program on solid footing.
Overall narrow body sales are extremely strong and wide body sales are well below expectations.

 

One Flight International journalist hypothesized a few months ago that potential customers are actually waiting to see more of the 777x (actual performance figures etc.) before making a decision between the 350-1000 or the 777-8. The-9 is actually alone in its 400+ seat market and replaces no previous 777 product. Once the 777X actually flies, it would unlock the 365 seat widebody market. (350-900 vs. 777-8)
What's puzzling to me is that Airbus was forced to build the 330-Neo because customers wanted a cheaper version than the 350-800. Yet, nobody is buying it. The ironic part is that the first A350 design would have actually been very similar to the 330-Neo. Until this was also trashed because of customer requests.

 

Cyn - I may be wrong - but I think there were only 8 orders for the A350-800, most from TAP. When the 330NEO was announced, it's capability was initially slightly less, but during development, it got a gr wt increase that made it's capability about the same as the 350-800. TAP switched their order. Delta is ordering 25 330Neos (and cut/deferred 350 orders by 10). It is a perfect 767-300ER replacement for east coast/Europe and west coast/Asia routes. The 350s are needed for east coast/Asia and west coast/Europe as I understand.

The 330 has been far more successful than its Boeing competitor the 767-400 - about 2000 sales to 41 sales...

Standing by for "incoming"!

 

You're right, the 350-8 was selling very slowly. I believe Hawaiian was the last one to cancel. I seem to remember that Airbus only launched the 330Neo after the 350-8 cancelation but I might be wrong.
From the top of my head, I think the 330neo is capable of 6750nm. I'm sure the 350-8 was way more capable than that since the -9 and -1000 are at around 8200-8300nm.
The market has spoken though.