From my experience living in AUS, Dallas, and Houston, I always preferred AA over CO.
I was elite on both and here were my experiences:

* The only advantage I saw with CO was being upgraded to "first" but over 2 years I was batting <50% on upgrades. This was even with checking in just under 24 hours.
* Food in CO's domestic first sucks. The pasta dish reminded me of Michelina's 99c frozen pasta meals.
* Food in CO's domestic coach reminded me of junior high food nuked through the plastic wrapper.
* That extra 2"-3" (More Room Throughout Coach) helps
* I was much more successful at getting flights with AA miles than CO miles. I don't think I EVER was able to book a flight for just 25K mi on CO.
* The best use of CO miles I found was transferring them to Amtrak and then redeeming them for retail store GCs. 5K miles = $50 GC. I'm not sure if this is still possible.

Regards,
-g