I like CO
I have been both an Executive Platinum on AA and a Platinum on CO. For years, I favored AA because the reward availability was much better. I also once found their First Class products to be comparable. I am fortunate to be able to book seats in FC, so upgrades are not a factor for me.
Starting around two years ago, AA basically eliminated FC Service, to the point where it was just a wider seat and free booze. I rarely drink, so the free booze did not matter to me. I still stuck with AA because the award availability was much better.
This year, AA Award availability has shrunken dramatically. I have not been able to find award seats to anywhere I was looking to fly unless I was willing to pony up double miles. My wife is a teacher, and my award travel times are rarely flexible, but I am often trying to book more than 6 months out.
The award availability is no better on CO. At this point, it does not appear to be good on any airline, because all of the airlines have sold out their frequent flyers by selling miles to credit card companies and others.
I now choose Continental because: (1) they still have full first class service and real first class meals on the flights I travel; (2) I like the whole Elite Access system; and (3) they actually seem to care about what their best customers think (reference them actually having a person responding to people here).
Next year, I will not be Executive Platinum on AA, and have certainly let them know why.