There are basically four types of deer that I would really want to see:
Chital: For an Indian section in a zoo, this is basically a requirement. Certainly in India they are the most commonly kept animal in zoos, and they are kept in many other places beside. They can also be mixed with a big variety of other animals, including elephants, rhinos and peafowl.
Visayan spotted deer: My favourite option for a Southeast Asian deer is this species, with its short legs and adaptations for dense rainforest. My local zoo has a breeding group of them and I find them one of the prettier deer species.
A smaller Asian deer: My top choice is the tufted deer (because it would really stand out with its jet-black colouring when mixed with the red panda), followed by the Chinese water deer. By contrast, the Reeve's muntjac does practically nothing for me - I've seen them alive twice in a zoo, but more often the only time I see them is as carcasses being fed to carnivores. They are also a really common feral species around here that come into gardens, so they feel even less exotic than fallow or red deer.
Southern pudu: The only non-Asian deer I have any interest in - would add an ideal species for South America that is not a tropical animal, and would also be an excellent option for a smaller deer.