From what I've observed I would say some of the common neotropical mustelids are difficult to keep in the sense of ensuring mental wellbeing in captivity.
This is particularly the case with the tayra and grison (although they breed fine in captivity) which are very prone to developing stereotypical behaviour.
That depends more on how they are exhibited, Mustelids are extremely active and do best in an enclosure like Nuremberg, but they typically get far less.