AA only requires 100K miles instead of 125K for top tier and they certainly treat their top tier a lot better. I forget if they get six or eight GU's a year that can be used internationally as opposed to four on Delta and they have a lot more inventory they can be used on. If an EP gets stuck in coach they get free drinks and food like sandwiches (I'd love for Delta to do that).
Unfortunately for me being Detroit based it is too difficult to switch to AA. I have too many non-stops here and hate the thought of connecting at ORD on most of my flights. There's also no Admirals lounge at DTW.
If I lived in a city like Chicago or LA or NYC where AA had a decent presence I would switch in a heartbeat