Originally Posted by Smiley90

google flights, set EWR/PHL as starting airport for a roundtrip on the same day, define non-stops/1-stops, restrict to UA, then it'll show you a whole map of prices everywhere that fits your criteria. (though you won't be able to restrict to "just mainline", but that's easily fixed by looking just at what's offered). With a fixed that that'll give you the factually best answer.