If you're CO eilte, I'd say flying COPA is a no brainer. They're okay, and you'll probably get a free upgrade.

Besides, AA is the pits. Don't know about SCL in particular; but in other South American countries I've visited, their people tend to be the rudest, check-in lines the ugliest (which as CO elite you won't have to worry about on CM), and red tape the worst. At least that's my experience.