I am biased, but I have to say that Ecuador, when I lived there was the best. When I say the best, I mean the best climate (Quito), the friendliest people, and the safest. It has ocean, mountain, jungle and everything in between.
I wish that I had spent more time in Peru (Southern and coastal archeological sites). I have not visited Chile (but been very close) and would like to. Bolivia was nice – never made it to Santa Clara, but I wouldn’t mind living in Cochabamba.
I only spent a short time in Colombia (the South, near the Ecuadorian border), but the people were nice, but there was a dangerous undercurrent that kept me away from other trips.
I spent a few weeks in Argentina (San Carlos de Bariloche, essentially Northern Patagonia close to Chile) and really enjoyed it. I only transited through BA, but it was a beautiful city that I would like to visit for a longer time. BA is too too big for my tastes, as is Lima, Peru, home of the brown skies. I been learning Portuges in case any jobs open up in Brasil – I would like to go, but the wife doesn’t.
Food-wise? The Ceviche in Peru and Ecuador is superb. That’s a good first course. I will agree that meat-wise, Argentina is great, but in Quito we used to go to this Brasilian Cuhasqueria (spelling) that was meat meat meat until you held up your hands in surrender. Of course, we used to go to a really nice Argentinian place on Amazonas. Depending on your location, the varieties of fruits is incredible. Chilean wine is quite good and pisco (my distilled spirit of choice) is cheap and plentiful.
One thing. When I was in Ecuador, I missed two things; baked potatoes and crisp lettuce. Potatoes were for Indians and the lower classes and the lettuce was treated to kill the bacteria. Coulda killed for a potato and salad at the Argentinian place.
Oh – On my way back from Argentina, I was packing a wonderful sausage for traveling snack. It was on the large (and salty) side. As there is hoof and mouth in Argentina and you can’t bring in their meat, I had to scarf it on the plane so that the DoA beagles wouldn’t take it. Seriously dehydrated.