I chose a350-800 because of the following reasons:
1. low fuel consumption compared to the alternatives with that capacity .
2. Slot in replacement for my 777-200ers and some of my 777-200lrs that are under utilized on their current routes.
3. Add capacity to under served routes in asia that are right over the max range of a350-1000, a350-900, 777-200er, 777-300er.
A general reason is also that most companies wihtin aws tend to keep their fleet commonality much higher then real life counter parts.
For e.g. big international airlines like air france, lufthansa, british airways, american airlines and delta all operate at least 6 or seven types.