New airlines can usually undercut older airlines because they don't have the same liabilities (pensions, debts from bad business practice over the years, etc.) and so they are usually great for a few years but then they evolve into the same shitty carriers that they compete with. In JetBlue's case, they were initially given a large tax break by NYC/JFK. When that subsidy expired they immediately started to charge for bags, reduce perks like better snacks, etc.

http://money.cnn.com/2015/06/30/pf/jetblue-checked-bag-fee/

There is a lot of competition. The article gets it backwards. It is the immense competition caused by consumers who fly mostly based on the lowest cost fare.

United's a pretty solidly middle-of-the-pack airline, like the rest. Delta has put a very strong focus on not having cancellations (favoring delays instead) and is rolling out an international Premium Economy service level, which is a huge step up.

Southwest is great for no change fees and free bags, but the cattle call boarding sucks, and they have far more "involuntary bumps" per passenger than United does. That said, because Southwest runs many short hop flights, you're more likely to be able to get another flight to your destination in short order.

Ask 3 people if they prefer United, American, or Delta, and you'll get 3 different answers. It depends so much on your home airport, what kind of flying you're doing, and so on.

I love Virgin and Alaska both, but despite flying 4-6 times per year, all of my trips were too short to qualify me as a frequently flier. By sticking with United (for longer flights, at least) I was able to qualify for their bottom-rung frequent flier program, and even just the possibility of getting a free upgrade on a future flight is enough to make me stick with an otherwise undifferentiated product.