Argentina or Brazil or both?

[Despairingof]

Looking at options for 15 days in 2023. Want to properly see both countries so tempted to split? Which would you choose and what are the must sees? Igazu waterfalls are included in either option.

i haven't been to Brazil so cannot comment but did go fir three weeks to argentina just before lockdown.
we. loved Buenos Aires and flew up to Salta then a road trip down to Mendoza.
it was very varied some v glitzy accommodation and some very basic. the most basic turned out to be the most fun!!
the scenery, people , food and wine were incredible. It was v cheap as well .
Happy to provide detail if that's helpful

Thanks - I think I need to do lots more research

Not both, you'll barely see anything. What are your main interests and when are you likely to go? If wildlife pick Brazil, if landscapes/walking etc pick Argentina.

I stayed 5 nights in Rio and then five night near Iguazza on the Argentine side. If you only visit one of the countries when you go to Iguazza you can visit the other and also Paraguay.
I travelled with tweenagers.

With 15 days OP can cover a lot across both countries if selective and plans ahead.

I recommend Brazil, our itinerary was

3 nights in São Paulo (would swerve - we were there for a wedding)
2 nights Iguazu falls (amazing - do the speed boat trip!)
2 nights Paraty (gorgeous, quiet, relaxing - beautiful hidden beaches and coves, would stay longer if I was doing it now)
5 nights Rio (Churrascaria we ate at was amazing - I think it claimed to be the oldest one, samba school was fun, obviously sugarloaf and the big JC!)

We were poor students so coaching rather than flying (apart from to the falls) so couldn’t fit in more but it was lovely.

Have the best time wherever you decide!