I'm sorry, but I have to disagree with this statement. Anecdotal, of course, but I will only use AA now for their BOS->DCA shuttle service and where I can find a cheap Y ticket to burn my remaining SWUs. UA's domestic F service has leap-frogged AA's given UA's new cabins mods, meal quality, and general service. Heck, AA can't even manage to get PDBs right, let alone on-time departures. As an example, last week we used AA to connect in CLT. Our upgrade wasn't processed at the window and I had to call the EXP desk three hours before the flight because we had also been dropped entirely from the upgrade list according to the APP. Upgrade went through only to get a mediocre meal on a plane which was filthy. Add to that the AC in CLT was disgraceful and a surly GA who challenged the dog's receipt for travel when the ticket clearly had the date and all the necessary info on it because she couldn't find the dog's PNR on our ticket. P-AA-thetic. As for AA at EWR: yikes! That AC reminds me of a Radisson in the early 1980s and the GAs are less than helpful...

DL, of course, has both beat, and given OP's home airport (EWR), I would take connections via DL too. UA clubs and general operations are a mess in EWR so much so that it makes IAD look like SIN or MUC. DL even has a nice little SC in EWR.