I wouldn't have put Cincinnati*'s hippo exhibit for more than just the obvious reason. But I say this as well because it was the final phase of Africa and after 11 years of planning, and over 5 years of construction, it's finally complete and Africa is now together as a whole. Still, despite this and it having my favorite predator exhibits in a zoo, I still would consider Africa a little weak. There just wasn't enough space to "transfer people out of Africa" like I've felt in Columbus. The only other one I saw was the much needed Tiger Passage in Cleveland, which definitely surpasses the quality that the zoo brings throughout the rest of the park if we were to compare it with their other exhibits.
Polar Bear Point and Elephant Lands opened last year while as far as I know Como Park's sea lion exhibit hasn't opened yet. Also you forgot Zoo Miami's Mission Everglades. I voted for African Grasslands but Polk Penguin Center, Elephants of the Zambezi, Zambezi River Hippo Camp and Mission Everglades are all among the best of their kind. However, I'll refrain from putting too much judgment until I see more of them in person.