Also, if you like the convenience that TW allows by flying non-stop LAX-DCA, and AA will most likely pick up this route, stick with AA. Otherwise, there will have to be a change of planes.

DL's BizElite is nice, and is offered trans-con from LAX to JFK and BOS. There is also a flight to ATL and CVG from LAX with the upgrades planes, but marketed as BizElite.

DL's upgrade policy is also tricky, you can not upgrade from the 2 lowest fares L&U. And if using miles to upgrade, you will have to buy an even higher fare ticket.