From a news article today. Surveyed 18 million passengers:

The results of the SKYTRAX 2012 World Airline Awards were announced Thursday at the Farnborough International Airshow, ranking the world's top carrier as well as bests in categories like "best by cabin," "best seats," "best lounges," "best regional airlines," and more.

During the 10-month survey period, SKYTRAX surveyed more than 18 million airline customers from over 100 different nationalities on their opinions regarding 200 international and domestic carriers.
Some of the results from North America include:

Best Low Cost Airline
1) Virgin America
2) WestJet
3) Southwest Airlines
4) Frontier Airlines
5) Volaris
6) Spirit Airlines
7) Sun Country Airlines
8) Allegiant Air
9) Interjet
10) VivaAerobus

Best Domestic Airline
1) Virgin America
2) WestJet
3) Alaska Airlines
4) Southwest Airlines
5) jetBlue Airlines
6) American Eagle Airlines
7) Porter Airlines
8) Frontier Airlines
9) Volaris
10) Spirit Airlines

VivaAerobus? Que eso? Never even heard of it.

Best domestic #6?

Conspicuously absent: UCH