CO isn't all that it's cracked up to be. Award inventory is scarce, upgrades on longer flights are practically impossible, and most "short flights" are on commuter planes (YYZ-IAH on an ERJ..mmmmm). I usually fly from BUF - where CO cares so much about its customers, that they replaced ERJ flights with a bottom-of-the-barrel subcontractor and we all know what that led to a month ago.
US may be far from perfect, but at least I can rely on being upgraded and finding good award availability with Star Alliance.