I've flown many different airlines and I have good feelings, neutral feelings, and feelings of absolute horror and disgust about some of them.
America West
This airline is okay in a pinch. The planes are rather old although I understand they're upgrading the fleet. The crew is friendly and courteous. Nothing to write home about, but they get the job done. I like the fact they offer "cheap" first class, and you can upgrade your coach tickets for a couple hundred dollars more. If choosing between AW and Southwest, TAKE AMERICA WEST!!!
United
San Francisco is United's hub and I have to say I do have a sentimental spot for United as she is one of the last few "ladies" left from the golden age of air travel. I've flown on the 777 and it is a beautiful aircraft and it was the first aircraft I had flown and encountered the entertainment system for each seat. This was way before the discount airlines started installing them in theirs. I also like booking my seat number way in advance online instead of having it assigned at the gate.
And I will always remember my trip to New York when I splurged for first class seats. WOW!! They fed us constantly, the service was impeccable, the seats were so comfortable, the flight crew addressed us as Mr. or Ms. with our last names, and they had a sundae cart where they made sundaes for you!! Oh, and they served milk and warm chocolate cookies before landing. I'm crying tears now just thinking about it!!
Frontier Airlines
My BF used to joke that this airline's ad phrase should be, "Where every seat's a saddle." But I disagree. Frontier is based out of Denver. Frontier is the airlines that has different pictures of animals you'd find in the west on the tail of each craft. So you might wind up flying "Coyote" or "Eagle." I wound up flying "White Snow Bunny." I kid you not. I thought it was cute.
They do have older models in the fleet, however the majority that fly in the Eastern US are newer Airbus models. So you should have a newer plane with comfortable seats with entertainment systems. The seats also have movable headrests as well. Crew is very friendly and they are expanding into many markets. So do give them a chance. I get the impression they hold Jet Blue as the competition and are trying to either match them or beat them. That should be a good thing for the flying consumer. And like United, you may choose your seat in advance online.
Continental aka Crapinental
Oy!! I had such a bad trip on Crapinental once that I make a concerted effort NEVER to fly her. Although the bad trip I took was in '95 so it's been a while that I can't remember why I hated flying her. But it must have been something really bad for it to stick in my craw. Guess I should give her a chance to see if the bad feeling goes away.
Southwest aka Air Moo
Last and certainly dead last is Southwest, otherwise known as Air Moo or Cattle Car Airways. I've flown Air Moo numerous times and I've decided that I don't care if their fares are cheap!! Yuck!! I'd pay more to avoid the rude service, the overbooked flights, the dirty and dingy planes, some of the passengers that fly this airline who are generally drunk, and their incredibly annoying staff. I don't need to be entertained in the skies thank you very much. And what choice does the passenger have when they're held captive in the air thousands of feet above the ground?
And there's no experience like the mad dash of passengers for the gate in order to try and get a good seat since there's no assigned seating. Be careful. The little gray haired lady seems harmless until you get her elbow in your ribs as she pushes her way to the front of the line.
If you think I'm exaggerating, try watching "Airline" on the A&E channel. Why on God's green Earth would an airline permit cameras to show drunken passengers, (almost every episode) crew that destroy luggage, crew that acknowledge overbooking flights, and generally giving the impression that flying this airline is the equivalent of flying a New York subway from the '70s and '80s?
If you have no choice but to fly Air Moo, may the grace of our heavenly Lord be with you. If you have another airline choice, GOOD GOD MAN!! TAKE IT!! THINK OF THE CHILDREN!!