It really depends on your travel pattern.
I usually can fly AA
And am willing to pay a bit more. Sometimes I can't. For examples from 2004:
NYC-Dothan, Alabama. AA
does not fly to Dothan so I had to take AA
to Orlando and then Delta the rest of the way.
was the ideal choice, and with the LGA
flight I took to get to Dothan I earned a AANYC cert.
IGR-BUE: I would have takes Southern Winds, an AA
partner, but everybody else was on Aerolinias Argentinas, so I had no real choice.
BUE-IGR: Aerolineas was the only flight I could take, time wise.
IGR-BUE: Southern Winds and AA
That's some of my 2004 flights. A majority of my travel is overseas, so I usually can take AA
to get me close to where I want to go, and then a local airline (usually an AA
partner) the rest of the way. If the flight is short I'll take an non-AA partner just to try them out. When I was in Madrid I took Spanair to Barcelona and Iberia back.