I did a redemption last year ZRH-SCL-EZE with Swiss on the long bit (which has a brief stop in GRU) and then Air Canada for the short hop to EZE. Swiss don't fly direct to EZE.

As to whether F is worth it over business, well I'd usually say yes but I don't like F on LH 747 as if you are travelling alone you have someone sat next to you. First class on Swiss (which I did) would be the best IMO. Depends on how many miles you have I suppose. Rememebr you can't do miles + cash with LH in F but you can with Swiss.

Swiss business is similar to LH business, although Swiss are due to get a new horizontal biz seat this year but the A340 that flies to S.America won't get them immediately.