At XNA we only have three options. AA, DL, UA. Have had too many bad experiences on AA, though it definitely controls the market from number of flights offered and has the most FF traffic. Not interested in flying on UA's E135/145s everywhere and have heard too many questionable customer service experiences. DL is a nice balance in flight/fleet options and I've never had a bad experience. May seem like too easy of rationale, but it is what it is for me!