Thanks for commenting
@Neil chace !
I'm curious about what you mention about the Goeldi' s monkey because these are usually not seen as too interesting by people.
Why are these strong contenders for you ?
Capuchins are a fascinating group and I find them very interesting to watch too because of their incredible intelligence.
The brown and tufted capuchins are very common here in this region of Brazil and of course they interest me but I think my favourite species would be the Buffy headed capuchin because of how threatened they are.