It should be mentioned that Longleat have the main indoor area that can be seen above for their original male and their three females. The male they got from Japan has an offshow indoors by the giant otters. As for outdoors, the one pictured is for the Australian male. The females have their own outdoors (shared with potoroos), and then the male from Japan also has his own outdoors which is onshow, by the entrance to the koala courtyard from the giant otters.
Having been to both, I’m going with Edinburgh. Both are decent facilities for koalas, but Edinburgh have (shockingly, given their reputation with the OTHER mammalian obligate folivore they keep) had an amazing breeding record with the species. I know it’s still early days for Longleat, but if Edinburgh have had so many joeys they must be doing something right.
EDIT: it should also be mentioned the Edinburgh photo shows only the female’s enclosure. If anyone could supply photos of the male ones too that would probably help some people. The Longleat photos show a decent overview, as the outdoors for the Japanese male and the females are more or less the same style of enclosure as the Australian male’s.