‘Argentinian’ is one of those words that has been used so often that the publishers of dictionaries feel obliged to include it as a word. It’s an example of usage trumping correctness.
The correct word has always been Argentine. I have never heard an Argentino call themselves an Argentinio, even though that is linguistically possible. In the end, it all comes down to style, preference and nationality (UK subjects will probably use Argentinian).
My personal opinion is that
Argentine is a more elegant word, in addition to being the most correct usage, and it is the only one of the three possibilities that I would use.
Also...not my words but the same apply.
My wife, whose from Argentina, tells me
Argentine is correct.
she also suggests I smack anyone who says
“Argentinian”.
So you've been warned.
