Taking investment aside (I'd then recommend Brazil); It depends on many factors, two easy ones are age and budget:Hockey_Nut said:To live....
I haven't lived in Santiago or Sao Paulo so:
to the younger end: Buenos Aires definitely, for the aforementioned reasons.
to the more experienced end: Uruguay nor strictly Montevideo is the most perfect place to go.
Lower: Buenos Aires.
Higher: Uruguay - even if young but can cross the river at will, you'll find Uruguay has none of the nuisances B.A. imposes, girls are just as pretty but a lot less snooty, and you can cross over to "the city" for 100USD .