Neither sakis or howler monkeys are kept in any of my local zoos (or any zoos in the country for that matter), but spider monkeys are. Just goes to show how much what is considered “rare” in zoos varies depending on where you live haha.
I think the white-faced saki is a good choice from an objective standpoint - any New World monkey is huge and the saki is indeed widespread in zoos from a global perspective. However, being not only absent from my local zoos but also not one of my favourite SA primates in general means that my personal keenness for them is fairly low unfortunately

Squirrel monkey, spider monkey or any of the three main tamarins (golden lion, emperor and cotton-top) would have gotten me considerably more excited.