If I ever listened to horror stories like these, there wouldn't be an airline left I would fly with. This is textbook; replace United with Delta, Southwest, Air Canada, etc., at will. The only company I've used that I haven't heard exactly this type of complaint about is Widerøe, a tiny regional line in Norway with a fleet of prop planes. This is unfortunate, as I live in Pennsylvania and get motion sickness on those little aircraft. And I imagine that if I spoke Norwegian—it seemed to me that while many Norwegians speak English, they don't do much complaining in it when the native language would do—I wouldn't even have Widerøe left.
It's also worth remembering that quality of service depends on a host of variables, including departure/arrival cities (major hubs are better than regional airports), routes, and times (morning flights tend to be less delayed, Thursday afternoon flying always a bit of a shitshow), etc.
I fly out of UA hubs frequently and have had nothing but excellent service from them this year (over 50 segments flown this year, ~60K miles).
Definitely helps to have status too...
Personally, I consider SW to the be shittiest of them all. I hate having to fight for a seat...
Lastly, use google.com/flights by far my favorite booking tool now.
I've been flying 1-2 times a month for the past year or so, mostly on US Air or American (same thing now) and I never saw anything approaching the level of problems United had on one trip.
Obviously, with travel sometimes things go wrong, but the quantity and severity of things going wrong at United makes me think there's something off about the way they're running their airline. For instance, the two times this year that they've had to ground all flights.
AA destroyed a piece of baggage of mine. They denied responsibility. I sued and won. Then I couldn't collect because that judgement was essentially nullified because AA was going through bankruptcy.
I have 1k status with United -- I fly internationally with them almost monthly. The problems I've had with United have been when bags have to be interlined to Brussels Airlines and occasionally (surprisingly) Lufthansa. I've also had Lufthansa somehow think it was a good idea for 2 toddlers to sit in scattered seats rows away from their parents (who were also rows apart as well, despite having checked in almost 24 hours before the flight and being Star Alliance Gold.) I've had Brussels Airlines say they were going to "gate check" a stroller only to have it show up days later. I've been stranded in Detroit back in the Northwest Airlines days when aircrews hadn't showed up to work. I've been stuck in Paris when the Air France pilots decide that salaries up to $300,000 per year just aren't enough. On a recent United trip from Hartford to Marseille, I was stuck in Hartford for % extra hours for an airplane that was stuck in Newark (just a <50 minute flight away.) I then missed a cascade of connections leaving me rather miserable. However, United sorted the problem and got me on my way as quickly as possible. Let's not forget Jet Blues antics on multiple occasions a few years ago: a 10.5 hour tarmac delay, a 7 hour tarmac delay among several other extremely long tarmac delays. AA had 14 long tarmac (over 3 hours) delays in February. United had zero long tarmac delays during the same period. Envoy/American Eagle was in last place for on-time arrivals last year.
I'm not defending United. I'm not disparaging the others. The fact is that the air transport industry is extremely complex and perceptions of quality are as varied as their are passengers in the sky.
Every airline sucks and every airline is great. Pick a day, pick a destination and roll the dice. When you fly often enough it seems like it all averages out to just one level of melancholic service; unless you're flying on Singapore Airlines -- then it just becomes sublime.
