Each of the big three do some things great and some things poorly and ime where one airline excels, the other two aren't as good.

For example, UA's app is the best of the bunch and maybe the best airline app in the business. DL's app is just okay and AA's app is not great at all.

DL's catering is the best of the big three currently with AA being somewhat in the middle and UA being bottom of the barrel.

AA's Admiral Club AAngels are the absolute best club agents, where UA's are middle of the road and DL's seem the worst of the group.

DL's D1 Lounges are a far ahead of UA's Polaris Lounges which have slipped a lot since they first rolled out with AA Flagship Lounges being the worst of the group.

In terms of FAs, DL wins hands down with the least amount of bad FA, while UA and AA seems to have a far greater amount of bad FAs, especially compared to DL.

UA does the best job both prediction the length of ant given delay and providing the cause for any delays while DL and AA aren't as good and both DL and AA heavily lean into the 15 minute creeping delays.

IME, AA's miles are right now the most valuable with UA's being somewhere in the middle and falling as Richard Nunn makes MileagePlus "Comcraptic" and DL SkyPesos are basically worthless.

So forth and so on.