IMO, DL is likely the best option if you don't want to stick with AA.

AS if the best program (still earn on mileage not spend, good redemption value, etc.) but if you need East Coast there is going to be a much more limited presence and the AA/AS partnership is going away (otherwise you could go AS and still bank miles when flying AA).

If you fly internationally, AS also has limitations in terms of alliance benefits (since they aren't in one) whereas DL gives you SkyTeam alliance benefits if you fly ST partners internationally.