Having not used LATAM before, and seen some bad reviews, I thought I'd counter that by saying my recent experience with using them to fly from London to Buenos Aires (via GRU) was pretty positive.

Hard product is very decent, It looks fairly swish and I slept well both times on these overnight flights.

Soft product was fine, the lounge at GRU is nice and modern, with great showers. On the flight the service was friendly, the wines good, reasonable IFE and ok food.

The GRU to AEP legs were in premium economy which is fairly similar to European business, bar the food and drink offering is lesser.