I would choose AA as well. When I lived in Chicago (went to U of C - is that where you are going ??)I was flying back to NYC a lot to visit family and concentrated on AA after UA just made me mad one too many times. On AA you can upgrade any fare, all miles from any source count towards your lifetime total and (hopefully) your lifetime elite status. All fares (except consolidators) earn status miles, and if you earn status you can start earning free upgrades.
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I Love New York -- Viva Espaņa