I really like Land of the Lions at London Zoo. Yes, its a waste of space, and of budget, and the cultural elements seem out of place in a historic and scientific institution such as ZSL, but I really like it. The langurs are brilliant, the lions always seem to be more active here than elsewhere, I love the aviary with the birds of prey, and even the Dwarf Mongooses can be quite entertaining.
By contrast, I always rush through Gorilla Kingdom. Too crowded to watch the monkeys, and the gorillas are never active. Meet the Neighbours (the aviary at the start, used to set the theme and create suspense) is delightful, with Madagascar Crested Ibis being a rarity in UK zoos, and sharing a walkthrough space with hornbills is always nice. I usually spend longer there than in the entire rest of the exhibit.