1. U.S. (Limited to Texas & Boston) 2. Spain 3. Argentina
Would really appreciate your help.
In my experience those are the biggest factors.
I find it hard to work with India because they are about 12 hours different from me, thus we are never in the office at the same time unless someone makes an effort to come in when they are normally sleeping. Working with Germany is almost as bad, we only get a couple hours in the early morning (our time) when we can catch them in the office.
When you share a native language communication is easier. (though be careful every once in a while some expression takes a different meaning in different countries). One of the best ways to get around this is set an office language and only hire people who know it (this might mean making all your people learn a different language)
I haven't worked with Argentina, and only minimally with Spain (meaning I might be wrong), but my understanding of both countries is their culture doesn't really understand time. In the US if someone says 9am they mean 9am and 9:05 will make them mad. In Spain/Argentina 9am might stretch as late as 10:30am and nobody cares. When the two cultures meet there is friction because of this. There are many other variations of problems where culture will cause two people to think the other is an idiot. It is worth learning something about the other culture.
Beyond that, my experience is you will find good and bad people in every country. Even if you could state that one is better than the other, you can find enough great people in the others as to not make a difference - if you are willing to search hard enough.
What I have found most helpful is airplanes. Every few months someone flying to visit the people on the other team is very helpful. When face to face you realize the other person is smart, not an idiot who can barely program (it is surprising how often this is assumed). Also when working next to the other person you see things they are doing that they are doing "because nothing else works" when there is a better way (or sometimes you know your tools team needs to fix something for the remote team).