I do this route a lot and split betweewn AA and UA. UA flys an A319 so if it is full upfront I will often take AA. My biggest complaint about AA on this route is even if they have a 757 they don't play a movie. Also make sure you sit towards the front of FC on AA East bound flights and towards the back on AA West bound (if you care about your food choice). UA really needs to get rid of aircraft with only 8 FC seats on competitive routes such as LAX-DFW.