I try to fly United whenever possible if for no other reason than that is where I collect miles. In addition, I have always had pretty good service with this airline. They have extra legroom on some planes, though not on all. Since I live in Chicago (United headquarters), there are always plenty of flights to choose from. I find it very easy to check in with the automated machines. If you don't have any bags to check, you can use one of these machines without having to wait in line - though with current baggage restrictions traveling with only a carry on is definitely more difficult on any airline. I have generally found the staff at United to be friendly and helpful as well.