Are you looking to drift around or settle down for 12 months? It depends what you're looking for. I spent 4 months travelling in ARG/CHL/URU. I didn't visit that far south in Argentina; said to be gorgeous but bloody freezing in winter!
First-world comforts? Santiago. Surfing? Pichelemu. Wine? Mendoza. Beer? Valdivia. Coffee and kuchen (German cake)? Puerto Varas. Serenity? Chiloe. Pacific coast? Valparaiso. Mountains? Salta. Homestyle cooking? Jujuy. Metropolis? Buenos Aires. Art scene? Cordoba. Students? Rosario. Small city feel in a capital city? Montevideo. History? Colonia. Casino? Punta del Este. Relax on the beach? La Pedrera.
If I was wanting a suffocating metropolis, Buenos Aires. For a mixture of culture and seaside I'd pick Valparaiso. For a mellow place to chill out and learn Spanish but close enough to a coastal weekend break, I'd pick Montevideo. Otherwise Santiago, Rosario, Cordoba, Mendoza would all be good choices for a longer stay. But it depends on your personality. I met a British man who'd spent 12 months in Salta La Linda - it's a beautiful place but small enough to do most touristy things in a weekend but what grows on you is the indigenous culture, living at altitude while being at the foot of the Andes and various extraordinary adventures by minibus.
I have not been to Chile, but I can tell you that Montevideo feels like a more relaxed version of Buenos Aires.
But cheap iPhones, for sure.
Uruguay is like a parallel dimension, where somehow Argentinean people didn't screw up their state. Still expensive though.
Lol....best Uruguay definition I've ever read
Not only iPhones, even groceries are cheaper and more diverse than in Argentina.
Yes, education costs are a problem but not for immigrants who work remotely (or don't have kids at all).
I could hop to/explore the EU, where I would feel completely comfortable and I could absolutely do with some minor bureaucratic hassle but I would be concerned about being able to working with a US job if I have that marked a difference in time zone (I don't know if that's actually a reasonable concern).
Wrt LGBT, I worked with people from Chile who moved to Argentina because the Chilean culture is very conservative/religious. In that case, Buenos Aires is known to be very LGBT friendly. I think Uruguay is also a good option (liberal/atheist culture), but simply because of the size, you'll have much more options to socialize in BA.
Wrt food, BA has lots of options from all over the world, simply because it's a very cosmopolitan city. Maybe not to the point of NYC (it's hard if you put the bar there) but certainly the city is also known because of the quality of the food, expect to gain some weight.
But of course, everything in life has trade offs, and this is where BA loses some points.. It's not cheap to buy technology there. That's why people who can travel, buy their gadgets and branded clothing in other countries.
Speaking of security, I was born and lived there most of my life, and the only time I was mugged, I was walking at 3am in 2003 (close to the biggest economic crisis in its history) in an insecure neighborhood outside of Buenos Aires (I had a fight with my girlfriend and left her house, and I thought: I'll walk home... This night could not be any worse, anyway... hehehe, I was proven wrong)
So unless you do something stupid, as I did, it should be relatively safe. But even then, you should take some cautions: do not use expensive jewelry or watches, be cautious when walking at night in places you don't know, do not leave unattended items (eg, your laptop at a bar while going to the wc).. Etc, some simple things that I've seen people who go there from other places sometimes omit to their regret.