I'll join in with the ones I've visited.
- North America - Tie between Brookfield Zoo's Great Bear Wilderness (Love the overhead bison path and wolf exhibit) and Cheyenne Mountain Zoo's Rocky Mountain Wild (Literally fenced in natural mountainside for most species and a larger species list) (Sidenote does Elephant Odyssey count?
if so that for me) - South America - Amazon Rising at Shedd Aquarium
- Africa - African Grasslands at Omaha's Henry Doorly Zoo (Just massive exhibits and a large species list)
- Asia - Asian Highlands at Omaha's Henry Doorly Zoo (If only for the takin/goral exhibit)
- Europe - I have not been to a zoo with a dedicated European complex
- Antarctica - Empire of the Penguin at SeaWorld Orlando (I did not go on the ride but the exhibit is amazing)
- Australia - LA Zoo's Australia area and Australia House (Massive night house for wombats and echidna. The outdoor areas are a bit dated but I love the foliage and the variety of species they have)