The ability to NOT have to deal with US immigration, customs, and then the TSA, and then a possible narrow-body front cabin even in F sitting nearly upright for a many-hours transcon (or near transcon) is reason enough to choose LAN. The fact that your LIM connection will be relatively painless and when you arrive in the US, you will be home at LAX. The hour of the early AM LAN arrival (600) is usually a pleasure for int'l arrivals.

I've written a report elsewhere comparing UA F (on a specific trip) with LA J (in the aggregate) on the SFO/EZE routing. LAX/EZE would be quite similar.

http://milepoint.com/forums/threads/...sfo-eze.20433/