I've been flying United several times a year between SFO and EZE, but I'm ready to give up on them for a number of reasons. For me, minimizing door-to-door travel time is important, and I noticed that American and Continental have the shortest flights: about 16 hours total time on the northbound through DFW or IAH. One thing I noticed at EZE is that the check-in lines at AA tend to be quite long as it has several flights. I also heard good things about CO's service (at least when compared to United).

Any other input would be appreciated.