Originally Posted by Billiken
For international travel - United (better upgrade policies).
For U.S. domestic travel - Continental (IMHO).
I always thought that AA had the better routes/times/fares to/from Latin America. However, my opinion is somewhat dated.
I am in Santiago as we write. After the terrible service and seats on AA's 767, I have vowed to switch to either UA or CO myself. Santiago is terrible for both UA and CO, but despite my love for Santiago and Chile, I rarely make this trip.
But I concur with Billiken. UA for upgrades and CO for quality. Note that CO upgrades are about as rare as a visit from the Tooth Fairy and their seats are cramped. UA is better but CO has a better network in the NE.