Usually, it seems any ungulate gets a high quality habitat. Big cats and aviary birds should follow. On the other side, I’d say bears (mainly grizzly) with their grottos and camels (dromedary) get low quality habitats. I don’t think I’ve ever seen a good dromedary camel habitat.
Maybe it is a European thing, but bears were actually my first thought for the 'best' category. I have seen bears of all eight species at around 20 collections, of which several keep multiple species, and on only two occasions have I ever been let down by the exhibit quality: Prague and especially Hagenbeck, both for Polar Bears. Beyond that, I have never seen a bad bear enclosure, and if I were to compile a list of the top ten greatest enclosures for any mammal species that I have seen, I suspect that at least three bear enclosures would feature. The
Browns at Bristol, the
Polars at Highland Wildlife Park, and the
Spectacleds at Zürich. But I would actually wager that of the 20 collections I refer to (I know not the biggest sample size by any means), roughly half of them keep at least one species in a 'world-class' enclosure, and none barring the aforementioned two are by any means insufficient. Even public parks or castles which keep bears, a long-standing tradition in several European countries, nowadays provide them with exquisite enclosures, a testament to the shift in standards away from pits that we have seen in recent years. Look at
Schloss Hartenfels in Torgau, for instance, or Bern, which I haven't seen in person, but looks to have improved drastically in recent years (no photos in the gallery but several elsewhere).
Most Snow Leopard exhibits are mediocre at best.
This is generally true, but there are exceptions, like
Zürich,
Highland or
Dresden. I think all of these far exceed 'mediocre,' but in fairness, they are exceptions, rather than the rule.