Question: How do you define 'best' airline?
This all depends on personal preferences. I break the 'best' airline category down into five distinct parts, judged on a scale of 1-10. My scale will be based upon flight route rather than overall airline, I find this is the best way to rate airlines as this is how travelers identify the best routes. At this point, airlines differ route to route as the aircraft you are should contribute heavily to the airline you choose.
Note: You'll note in this list I do no include price. Airline prices vary so heavily on time of booking, route, and aircraft. I'd much rather rate based on quality not quantity.
1. Quality of Seats (Per Class)
I will break this down by class, where I can with a certain trip/airline. Additionally, where I can only compare to a specific class, I will compare the to other fleets of the same class/price.
This will entail specific aircraft, seat width, seat pitch, recline/lie-flat, storage, and cabin space.
2. Quality of Entertainment
This is a large part of the in-flight experience. I, like many, use this time to either work or relax. Therefore, WiFi, on-demand entertainment, power ports are considered in this category.
3. Quality of In-Flight Food
During short or long haul flights, I often eat in-flight. Those that enjoy flying understand that the food and drink is in large portion a heavy factor in a specific flight they may choose.
4. Quality of Customer Service
I myself work in a fast paced start-up world where I am responsible for Customer Support and Success. I know what customer service is and it's principles apply to any business.
This category is critical because when traveling for business or pleasure you need to be able to change flights quickly, for little or no cost, and to be able to actually speak with someone.
5. Quality of Fleet
In the age of WiFi, lie-flat seats (and in some cases suites), necessary power ports, and overall service. The fleet of an airline is a heavy factor in my decision of what to fly.
6. Flight Access and On-Time Reliability
How many flights are available per day? What is the on-time reliability of those flights? What about the boarding process? As a business traveler, in my mind these key to know.
7. Lounge Access
Whether flying First, Business, or Economy (Coach in old-school terms), we all enjoy access to a lounge. Now, lounge quality is an entirely different ball-game. I will do my best to describe the lounges, but for now I specifically will rate this category based upon level of access. Some are allowed access only if flying first, some are allowed if of a certain status. I shall rate those here.
8. Overall Quality
First thing everyone needs to know is upgrades are not guaranteed. I'll say it again, upgrades are not guaranteed. Therefore, my personal opinion is that the best airlines have a balance of quality in any cabin on their airline.
As an example, let's take United vs. Virgin America. Two domestic US airlines. The route also matters, let's take JFK to SFO, a route I often fly.
First Class: Leather seats, reclines fully, food choices are decent, entertainment is average.
Economy: Seats are cotton, recline slightly, food is poor. Overall experience is sub-par.
Overall Rating: 3 (Aka you better hope for that upgrade)
First Class: Leader seats, reclines fully, food choices are OK (not great), entertainment is excellent.
Economy: Seats are leather, recline more than typical economy, food choices are excellent and on-demand, entertainment is excellent.
Overall Rating: 10 (I'd fly this economy class over United short-haul business class)
Therefore, the way I rate my first category is by overall cabin quality. For any cabin I may be sitting in, how is the experience.