Well, both landscapes are extremely differents.
In Iguazú you ‘ll find the waterfalls, too much green nature, birds, coatíes, a lot of typical animals and in Oct it may be a little bit hotter (the weather there it’s sub.tropical without dry season).
The Glaciar Perito Moreno it’s in the south of the country, i didn t have the opportunity to go but i ve seen pics, and it’s amaaaizing, the huuuge blocks of ice. The weather it’s cold and in oct it may be still very cold.
Both are unique, it depends on what you like most.

Since you are spending so few days i recommend internal flights , so you can take advantage of the time.
Anyway the bus service in the country it’s veeery nice.

If you need any more information, pls tell me :)

best regards,
andre