If I had an airline,
I would chose to be a Major International airlines as I believe super big airlines are less prone to collapse because they have a lot of assets and they can easily recover if their management staff does the right thing to help the company recover.
My Airline Fleet would consist of (depending on which plane I would get a better deal and how much money I would save for using that plane and other factors) :
[Short Haul International/ Domestic]
-Airbus 320-200
-Airbus 321-200
-Boeing 737-900
-Boeing 757-300 (or any plane that can carry around 240 passengers for two classes, and it will be used for High Density Domestic Flights/ High Density Short haul international)
[Medium Haul International]
-Boeing 767-400ER
-Boeing 777-300 (High Density Routes Only)
Boeing 787-900
-Boeing 787-1000 (High Density Route Only)
-Airbus 330-300
-Airbus 330-200
[Long Haul International]
-Boeing 777-300ER
-Boeing 777-200LR (For Ultra Long Range Flights)
-Boeing 777-800
-Airbus 350-800
-Airbus 340-500 HGW (To supplement the Boeing 777-200LR fleet)
-Airbus 340-600 HGW (To be a temporary stopgap measure until the 777-800 or another twin engine plane that can have the 777-800 passenger capacity/range arrives)
-Airbus 350-1000
[Long Haul International/ High Density] (use for any routes that my long haul international fleet may not be able to carry the whole load)
-Boeing 747-800 Intercontinental
-Airbus 380-800
(These two planes would be situational depending on which routes and how I think my profit per factor I have, if the 747-800i is better because of the profit factors, I would have it run on the routes it serves better, the A380 is the same story, profit factors line up more than the 747-800i, the A380 will fly then.)
That is my fleet if I went by our era's passenger aircraft.