I did a NYC-EZE flight a few weeks ago. Flew down on AA from JFK-EZE in J. Couldn't believe how bad the front cabin was--AA is simply not competitive on seating, meals, service, etc.
I had business in the midwest, so I did the flight back EZE-GRU-IAH on CO. What a difference.
btw--2 of my co-workers go violent food poisoning on the AA return flight EZE-JFK. They flew on different days (one on a Tuesday and one the next day), but had exactly the same symptoms--they both thought it had something to do with bad eggs at breakfast

Sounds like you were traveling on paid, o/w, business class tickets? If so, that gives you considerably more, and different, options than the OP here. There is no question that CO's BF is much nicer than AA's J-class (but nowhere near as nice as the F-cabin that AA flies to some S. American Cities from JFK-- EZE not being one of them (GRU is) and you can upgrade to F from paid J for only 10,000 miles, which is a great deal.) So, if the OP has several thousand dollars to throw around, I'd certainly say CO is the way to go in this instance-- the connection notwithstanding. But if the question is as I understood it, using miles to upgrade a discount economy ticket to get the most comfortable ride for the best price-- it's CO Y-class vs. AA J-class for many fliers, due to CO's international upgrade policies. Plus AA will still get you to EZE quicker and with much less hassle.

As far as the the food poisoning goes... I think all airlines have some instances of food poisoning and I sincerely doubt AA was trying to kill your co-workers on purpose-- but I could be wrong on all counts. http://www.flyertalk.com/forum/smile.gif

You can also fly Delta to Santiago Chile. Then hop on either LAN Chile or Aerolineas over to EZE. There are also some European airlines that fly the route. I think AF and LH stop in EZE on their way back to Europe. It's a beautiful flight over the Andes.

JohnSmith - I'd be interested in knowing how you flew CO from EZE. They don't fly there. I'd guess you got something else to GRU and took CO from there.

I'm flying IAH to EZE Sunday. Looked at options to earn OnePass miles, but ended up flying Argentina Aerolineas via JFK. AR out of Miami was sold out. The fare was more than $2000 cheaper than CO to GRU and Varig to EZE. More than $2500 cheaper than AA/UA alternative. The $3900 Condor Class fare was comparable to Copa's via PTY, but to earn the OnePass miles on that route would have required overnights in MIA to and from. Plus travel is on 737s w/domestic-type 1st class seating. Aerolineas is int'l business class. First time on AR - ought to be interesting.

I didn't think AA was purposely trying to kill my co-workers, but if they were, they made a decent attempt http://www.flyertalk.com/forum/smile.gif It wasn't a pretty site from what they told me. Both of them got violently ill within an hour of leaving JFK (again separate flights a day apart) and wound up having to pull off to the side of the road to deposit some of AA's special food.

Yes, I was on multi-thousand dollar o/w tickets. I flew JFK-EZE on the way down on a discounted J class fare of about $2400 and EZE-GRU-IAH-xxx on the way back for about $3,000. I flew EZE-GRU on Varig which was fine, nothing spectacular, but totally acceptable.

I also flew a quick sidetrip (EZE-MVD-EZE) on AA on their 767 which does a MIA-EZE-MVD-EZE flight. Very funny flying a 767 for about a 75 mile flight at the altitude a ERJ usually flies.

Just a heads up. In June, Copa is initiating JFK-Panama service, and the flights do make good connections to Buenos Aires. Certainly now a plausible routing from NYC. The drawback is you have to fly in the daytime, leaving JFK at 6 am (ugh) and returning at 1:43 am (double ugh). You also have the pleasure of a 5000 mile narrowbody flight, although I personally find Copa's service to be quite good.

Not sure they're pricing the routing yet, but it's likely to be competitive with what's out there. Elites would be eligible for FC upgrades. For those redeeming points, New Yorkers now have the advantage of not needing a CO connection (Copa is usually MUCH easier to find reward seats), and it's only 35,000 miles in coach (a ff bargain!).

Sfo-eze
 

About 10 days ago I got a standard award (!) first class SFO-EZE for a May 12th outbound. The segments SFO-IAH-PPY are on CO and the PPY-EZE segment is on Copa. The routing requires an overnight in Panama City in both directions but that was ok with me so I opted for two extra days in Panama as I haven't been there before. You must call to get a reward CO/COPA to EZE as it's not available on CO.com.

Sometimes, American operates both of their 2 daily MIA-EZE flights with 777s... when this is the case, the EZE-MVD leg is also operated by a 777 - how's that for a big bird on a little flight?!