Welcome to CO/OnePass!

I think generally you will find a superior experience to AA, particularly on your domestic travels, and particularly if you are comped to Platinum.

The one main issue with OP is the difficulty/expense of obtaining international upgrades, but that gap has narrowed somewhat with the recent changes to AAdvantage.

In terms of international premium class travel, CO BusinessFirst beats AA Business by a mile, and the only drawback in a comparison to AA First is the lack of truly flat/horizontal sleeper seats. But given AA doesn't even offer FC on that many routes anymore, it isn't such a big deal.