[leojg]

In terms of connectivity and living expenses three are more or less equal.

As an Uruguayan I would say that Montevideo is nice, but there is not much natural beauty around, the same for Buenos Aires, but Santiago is in the foot of the Andes, so in that it has more to see.

Also Montevideo is quieter than Buenos Aires but Santiago is much more well organized than both. And the only one that don't have a metro train system, so the public transport consists only on buses that get quite crowded on rush hours.