I'd like to go to South America for Xmas this year, 12/19-12/25.
I'm thinking Buenos Aires for a few days, and maybe something else?
UA shows availability to EZE for those dates, but what would be a good place to go from there?
I was thinking an open jaw or stop-over itinerary.
I'm open to Rio or Lima or Santiago, or something in the Argentine interior.
Suggestions?

I think Easter Island is a popular destination. What are you interested in? I've been to Ushuaia and loved it; small interesting town, fun national park, southernmost city in the world, etc.

for a short trip like that, I'd rather visit 2 cities, like BA and ? - would pretty much depend on availability of reward tix with non-stops (in-bound will likely be a redeye and off to work).
UA has avaibility to and from EZE, but not from MVD or GIG. I should have enough AA avios to use one-way redemptions. Non-stops are a must, but a stop-over would probably be a better idea.

Iguassu if you haven't been.
Rio would be fun for around NYE but you won't get there on miles (I don't think).
Florianapolis if you could get there, if not, Porto Allegro and take a bus.
Or just take it easy and take a ferry to Uruguay to visit Punta del Este. I believe it's about 3 hrs from Montevideo, but there are many other nice coastal cities closer to MV.

uraguay has beaches & is close & easy to get to.....

baraloche is fun for a short stay, but wont work for an oj on *A iirc....

the falls are worth the trip, but you would want to cross into brazil to see both sides....

lots of info in destinations under travel & dining....

Have you considered Mendoza, AR? If you like food and wine you can have an awesome time in Mendoza. Its close enough that you could add it to your plans and not be overreaching.
I would encourage you to avoid Santiago, Chile. We really loved Buenos Aires and found little to do in Santiago. Most exciting thing was an earthquake.

Iguassu or Mendoza would be the obvious other places to go in Argentina, although there are other possibilities depending on your interests.

MVD or Punte del Este.

Fabulous at that time of year. Great at any time of the year

OK, so MVD seems to be the winner.

No one flies there direct from NYC though.

Not so sure about MVD being the winner. I liked it there -- a lot -- but Iguazu Falls is spectacular. Go there.

Leaving 12/19 you won't get there til 12/20 at ~9:45am.

That leaves four days in Buenos Aires before flying out the night of 12/25.

Iguazu Falls can be done with only two full days but you should see the Brazilian side as well and that would, YMMV, require a Brazilian Visa.

Cost of: 15,000 Avios for Roundtrip AEP-IGR or $240 for your dates.

Mendoza is also a great city to stop for a drink at some of the famed Bodegas, winery, of the region. They also have great countryside day trips (Aconcagua highest mountain in Americas), horse back riding and more.

Cost of: 9,000 Avios Roundtrip AEP-MDZ OR $315 for your dates.

Uruguay is a great choice as well. With Pluna, Uruguayan airline, going out of business you are pretty much limited to Aerolinas Argentinas, Sol Lineas or Buquebus (boat, bus and planes).

Two examples of Costs: Colonia for ~$55 in a 1 hour 15 minute Buquebus boat ride
Punte Del Este for ~$300 for 50 minute Aerolineas Arg flight.


And that is just the tip of the iceberg for Argentine travel.

I am not sure how you like to travel and if you can do quick day trips or not.

I hope some of the information is able to help you make a decision but I don't think you can go wrong no matter what you choose.

Thank you so much!
That's very helpful. We are nomadic travelers, and enjoy moving from place to place.
All of your suggestions are test options, it'll be hard to pick just one.
For the Mendoza flight, how would you recommend booking it with Avios, AA, BA, or other?