I want to stress this as someone whose background is in International Relations (not specific to OP, just people in general) that it's never a good idea to mix passports. Keep the following in mind to avoid problems:
- ALWAYS use the same passport to enter and exit a country, not just Argentina, any country. This is often the law in many countries, and in less liberal ones you could be accused of anything from flouting immigration laws to being a spy for having multiple passports/mixing them up
- Use the passport of the country you would call 1st if you needed consular assistance
- Use the passport of the country you would prefer to be deported to in case you are denied entry for some reason
- Remember, your country of citizenship may require you to enter the country with your passport from there, and airlines don't always know this (IIRC Brazil is one of these countries, and as such won't allow you to enter on say an Argentine passport even though you have visa free access/residency on demand)
- ALWAYS use the same passport to enter and exit a country, not just Argentina, any country. This is often the law in many countries, and in less liberal ones you could be accused of anything from flouting immigration laws to being a spy for having multiple passports/mixing them up
- Use the passport of the country you would call 1st if you needed consular assistance
- Use the passport of the country you would prefer to be deported to in case you are denied entry for some reason
- Remember, your country of citizenship may require you to enter the country with your passport from there, and airlines don't always know this (IIRC Brazil is one of these countries, and as such won't allow you to enter on say an Argentine passport even though you have visa free access/residency on demand)