I agree with mlibers, but mainly for one reason. Strike. Aerolineas is having several union problems at this time and strike may "strike" your trip. Take a look at the English newspaper buenosairesherald.com for further info or updates (should they be news).

However, there are several destinations where Lan Argentina does not fly (yet). Lan is a member of oneworld.
There aren`t many choices inside Argentina either regarding earning miles. You are pretty stuck.

Good luck