Same here. I have flown DL and AA, mostly during UA irrops and have not found them any better. I was put in RJs which are no better than UA. And I know that DL's Skymiles is horrible - I have a bunch of Skymiles which so far have been unable to redeem for the dates/times I wanted, except with the highest redemption miles.
On AA, the service was better, but their FF program is tied to BA's for international to Europe and SE Asia and BA/AA add fuel surcharges for flying. Sometimes the revenue ticket was cheaper than using the miles. May be AA is somewhat better if I fly them enough, but from and to IAH/DEN/SFO my options are limited.
Only WN is better, but due to their lack of international ops, I have decided to stick with UA for now.