I'm quite interested to hear people's opinions on this, I've only visited two zoos with apes in Australia (Adelaide and Melbourne), except for Monarto where the apes are not yet on public display. My favourite out of the ones I've seen with have to be Melbourne's gorilla exhibit, although I think the bachelor group could have a nicer enclosure
I would say Melbournes two exhibits although I think Monarto could easily take the honours once I check out there chimp exhibit when it opens. I would also like to see Perths orang-utan exhibit...It looks pretty good but I won't get a chance to head over there for quite a long time.
Melbourne's gorilla and orangutan exhibits are both better than the similar enclosures at Taronga, but the Sydney zoo does have a large chimpanzee habitat that is packed with those energetic apes. Adelaide's pair of gibbon exhibits are perhaps better than the orang exhibit in South Australia...but as Pat has mentioned the plans for Monarto's chimpanzee enclosure make it appear to be amazing!