As a AA EXP living in Dallas, DL should be my backup. My problem with them is two fold, first, if I have to sit in coach they have a bad coach product compared to AA and my backup UA. Second, they have horrible upgrade rules for international flights, M class or better, which can get real expensive. So I live, at least part time in a DL hub city and can't figure out how to use them as a backup, let alone my main carrier. Just my 2 cents.