I really only fly two airlines, American Airlines and Southwest. I did fly United once, but was not that impressed with service and all of that (only flew United cus I priceline'd it). AA has really good customer service and there AAdvantage program is one of the best frequent flyer programs bar-none.
But Southwest in my mind has the very best customer service in the industry. All of their flight attendants have the best additude and as much as they might be a no frills airline, they are still really fun to fly.
Being that I live in the Southwest of the United States and Southwest is a major carier here at the Albuquerque International Sunport (Sunport is the samething as a airport, just more sun) I fly them for a lot of my short-hall flights.
Going to Phoneix, LA, Las Vegas, or anywhere in between, Southwest is my choice. Now when I start to go back east is when I have to figure out if I want Southwest or AA. The big factor is where am I going, and cost.
If I am going somewhere where I will be on the plane for a long time, I might go with AA, as I love there "More room in coach" program (even if they have scaled it back in the wake of 9-11). Also I must say that as I get older, I find I like having assigned seating. Yes, part of me loves getting to the airport like 3 hours ahead of my flight to get in southwest's "A" boarding group, but it is also nice to know that I will have all window seats on my flights too.
Anyway, in about 2 weeks I am flying up to Cleveland to see my sister and so we can both goto the Barenaked Ladies concert. Flying up and back I am flying American cus they were the cheapest option. Now come December, the whole family is flying upto Clevleand to have christmas with my sister, and again I am flying American. This time I am flying AA cus I change planes @ DFW, where as if I had flown Southwest I would have been changing planes in Chaigo-Midway. As much as I like Midway as an airport, I have friends in the DFW Metro Plex area and DFW is less-likley to get closed due to snow.
Now flying into Cleveland, I can not control the weather, but I can choose the best hub / airport to fly into that will reduce my chance for snow.