I look at two categories - table stakes and differentiators.

Table stakes:
- Operationally efficient, reliable, safe
- Reasonably good global coverage through its route network plus alliance or partners
- Adequate comfort per at least the modern standards for Y and J. Includes a standard business lounge for J.
- Good website and the ability for any traveler to buy and manage their itineraries online from anywhere in the world

Differentiators:
- Better-than-average soft product in Y and J.
- A good true F product/service. Includes a premium lounge offering.
- A true premium economy offering
- Extensive route network on its own metal, including regionals if they are operationally integrated
- Good FFP - rewarding, easy to use, easy to redeem online
- Extras such as generous routing rules, free stopovers at their hub cities, ground transfers for J/F pax, etc.