I do South America quite frequently (BCN based) and usually search other EXEU options but as of late leaving from BCN has been the cheapest. BCN GRU is on the new A350 and you can connect depending on the date and times wide Bodo GRU-SCL. Mind that my usual destination is MVD or PDP will also add that via US is a great option I find it refreshing as said to break the trip either in JFK or MIA.
ON LATAM avoid the 767 as they are not lie flat...
Best, JC