I've never flown either.
I've flown Delta, American, Northwest and Airtan though.
Are the service and prices that bad on United and US Air?
I was a 1K (100,000 miles flown is a single calendar year) flyer on United. Always flew first class though. Service there was fine.
I have gotten some good deals on USAir from consolidators. Their service struck me as the equivalent of Delta or American.