Brent, I'm actually in the process of moving to Santiago after 1.5 years in Buenos Aires. I've visited Santiago about a dozen times, and finally made the decision based on some of the following:
- Proximity to the outdoors: Many people have already mentioned it, but easy access to the outdoors is long and expensive. Mountains and beach are easily within 1 hour of Santiago, and given this, it's obviously much cheaper to enjoy my outdoor hobbies
- Stability of currency/potential of future growth: Although dani28 mentioned that more multi-national corporations are in Buenos Aires, the possibility of getting jobs there is virtually impossible, as they require residency before accepting you as an employee (which if you read the other threads on this top, you'll find to be quite difficult). Chile, on the other hand, requires little more than a certified college transcript (to enter as "Professional"), and will allow you to first find a job then apply for residency legally. I also find the cost of living to be a bit lower in Santiago, and given their more stable peso, makes a difference for my pocket at the end of the month.
I wouldn't be honest if I didn't point out a few things that are definitely different from Buenos Aires:
- Nightlife: This doesn't sound like it's a priority for you, but unlike Buenos Aires' bars (which almost never close), Santiago is all but dead on Sundays (honoring the Catholic tradition is much more entrenched in the culture) and bars/nightlife is much less vibrant. I still have a great time on the weekends, but if you're into the heavy partying that Buenos Aires can offer, then yes, Santiago's scene will seem lacking. As far as food, I'm a trained chef, which means my opinion on food is supposedly well-qualified, and I think the food in Santiago is excellent and more diverse in types than Buenos Aires. However, there are fewer restaurants, meaning that the diversity itself is of a smaller sample size.
- Ability to make friends: I've been told, but personally haven't had much time to try making new Santiago friends, that the Chileans are a more closed-off society. Even some of the Argentine/Uruguyans who moved to Santiago said they had trouble integrating into society. That said, I'm an expat in both countries, so I figure that I have to work harder at making friends in either place than if I was from South America.
- Feels more like a Western City - Not sure if this is a positive or negative, but for better or worse, Santiago (in parts) definitely feels like a city in the US. Buenos Aires has parts that feel more like Europe, with respect to architecture. In fact, Chile has a bilateral trade agreement in place with the US, whereas Argentina doesn't trade nearly as freely, and I think this has an influence on the overall "feel" of Chile.
Either way, I like both cities, and they each have specific things to offer. Based on what you said about activity, Santiago is definitely better (although there are shuttles to the mountains & beaches, but renting a car is pretty easy & faster too). Good luck!