This thread is a bit long to read @ 2:47 AM, so sorry for any redundancy.
A vote for Medellin if you're looking for other expats (I typically don't and go for experience instead). I was there for all of last month.
NOTE - I found it very polluted. On the level of Seoul. Maybe worse, given its size. This is why I left. I had sinus infections and sore throats... But I'm a bit sensitive at the moment.
Also, it dangerous. Not bad. I wouldn't have left because of this, but you shouldn't whip out our cell phone while in public. I knew a few people to get robbed while I was there... And this is during just a month. Only Rio seemed worse in my experience.
I also spent 5 months in Buenos Aires late last year / earlier this year. It was great. I really enjoyed my time there. Definitely travel around to see Valparaiso and Patagonia if you're already that far south.
BA is rather safe if you're in Palermo (I'd walk around at 2AM with headphones in), but note it is getting worse by the day. I have a full time employee still there.
Because of the currency situation, you need to bring in cash. You can always hop over to Uruguay to get more cash from the ATM. But bring in Dollars or otherwise, makes your money go literally 50% farther. It is easy and safe to exchange on the Dolar Azul market.
My Venezuelan friends say that it is going the way of their country. So now may be a good time to go. Before it is crazy dangerous, if their predictions come true.
Otherwise, I spent 6 months in Mexico, mostly last year. I would suggest Sayulita over Playa Del Carmen & Puerto Vallarta.
PV is very old. And I didn't have much fun there.
PDC is young and awesome. But the internet is bad. If making calls is really important, I wouldn't recommend it.
Sayulita, should have decent internet. And great surf. Plus you can get organics delivered from PV (it is 45 min north). And there are lots of young backpacker types always coming through.
If you go to Mexico, get some Tacos Pastor for me.... Mmmmmmm.