If you are not concerned with status or free flights, I would go with AA. United only has more legroom in Economy+. You have to have status to get these seats, and even then you are not guareenteed that you will get one of these precious seats - especially if you change flights at the last minute like I often do.
AA has MRTC so you always have a decent amount of legroom - as a tall person I really value this wherever I sit.
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I Love New York