Sumatran orangs (in my opinion) make a much better exhibit, in captivity they are far more active than Borneans. Compare the two species at Chester for example- the Sumatran group is really interesting to watch, while the Borneans just sit and do nothing. Its a pity Paignton have Borneans.
Obviously because of my strong attachment to Bulu and her family I can't agree with your last comment! I haven't seen enough Sumatrans to compare them. The Twycross orangs seem more active than Paignton's and when Gigit came from there, she really stirred things up. Even Bulu climbed up to the high platforms indoors.
I can understand where you are coming from. One of the problems with the Paignton Orangs is Bulu and Senja in particular had spent very many years in traditional cages at London zoo- and even to start with at Paignton too. I remember Senja was so obese she could hardly get off the floor in the Le Fevre House. So they are a particularly bad example. Its interesting you say that Gigit stimulated more activity among them too. Do you know how why Gigit died? i Heard she was frightened of Nakal and fell or jumped onto concrete.
I can promise you Sumatrans are always far more active- given the correct climbing equipment they will utilise an enclosure far more. Even an adult male Sumatran will do cartwheels and brachiate high up if ropes and handholds are provided.
For me its not so much wanting entertainment from them, more knowing that a higher level of activity means they are interested and stimulated by their environment.