I'm in the initial stages of planning an urban vacation to South America. Anyone been to both Buenos Aires and Santiago and can give me your preference, and why? Thanks.

No comparison -BA wins hands down. Better food, architecture, culture. Santiago is a let down, smoggy, laid back and not even a spot to spend much time when you are visiting Chile. There are many better options in Chile than Santiago, whereas BA, is tremendous(labeled the Paris of the South)

Another reason why BA wins: $$$$$$$$$$$$$

Much less expensive than Santiago.

Been to both and we always compare them this way:
-BA is New York: hot, humid, sophisticated, old un airconditioned subway, great food, great nightlife, big sprawling city that ignores its spot on a river, nothing special in the way of geography, run down but not dirty, and very inexpensive, and more crime than Santiago. A beauty that grows on you. Cheap antiques.
-Santiago is LA: great dry climate, spectacular mountains (when you can see them), great beaches close by, great mountain resorts close by, very clean, in much better shape than BA, very safe, excellent subway, inexpensive (I live in NYC, they are both bargains to me, though BA is cheaper), we had some great meals in Santiago, nearby vineyards. Cheap antiques.
Lots of good day trips out of Santiago, and we never leave BA when we are there, going back at the end of the month.

Doledrums.....could you expand on your comment that there are many better options in Chile than Santiago.....planning on spending approx 4 weeks in a SA city next Jan/Feb - considering Santiago or Buenos Aires.....then travel to Easter Island, Macchu Picu and Galapagos......thanks