When it comes to transcons on F & J definitions vary. Delta & United don't have an domestic F product on this route. Instead it's a version of their international J service with lieflat beds and multi-course meals ect. AA flies 3 class A321s on the JFK-SFO/LAX routes where both J & F are based on their international products with lieflat seats & upgraded meals. B6 flies their Mint product which is of Business class level with lie flat and multi-course meals (no lounge access yet). VX flies their domestic F product which is quite good for a domestic F but fails next to the others.

So AA's F wins because it's the best F product on that route but it's also comparing apples & pears.

UA has the most frequency fro EWR-LAX/SFO.
DL has a solid product but on generally older widebody aircraft. Some like the widebody factor.
AA has new planes that are 3 class on this route.