I'm new to FlyerTalk and thinking about switching to United Mileage Plus from American. Sorry if there's already an existing thread, but I would like a good blow by blow comparison before I make the switch.

I fly mostly domestic coach and some international paid business class. I do care about upgrades. I'm currently a Platinum Advantage member and already have the matching elite status (Premier Executive on United). Any compelling reasons why I should or should not move my business to United?