Another vote for LAN. Especially since you're going to the Southern Cone. Nonstop widebodies from USA on LAN vs. multi-hops and narrowbodies.

Also, LAN is in oneworld, which means miles earned can be credited to or redeemed on American and the other oneworld carriers, and count for elite status. Depending on travel patterns, you may be better off crediting them to LANPass or to AAdvantage, if not already committed to a oneworld program.

Some intra-country LAN discount fares don't earn any miles on AAdvantage, while they do earn kilometers on LANPass. One of the reasons I accrue on LAN instead of AA. Also, LANPass does not have the restriction against earning/redeeming on British Airways for USA-UK flights that AAdvantage has. Like AAdvantage, LANPass also has non-oneworld partner Alaska in the program, and not-yet-oneworld Mexicana, so you have a lot of North American options.

Finally, and without giving too much away, LANPass seems to have a bit of a problem with the miles-to-kilometers translation for minimum miles on AA flights under 500 miles. Which is a good thing