Originally Posted by MileKing

You're missing the fact that standard award seat availability on CO is atrocious. Award availability is very poor for U.S. domestic tickets and near impossible for business/first class overseas. Unless things have changed, I believe that using miles to Europe on Fridays and Saturdays during summer months is not permitted.

Before making the change, do yourself a favor and directly compare standard award seat availability for AA (or US, where applicable) and CO on routes you would consider redeeming miles on. A smattering of random dates will suffice. You will likely see a huge difference.