My opinions as of 2024 (habitat animals only):
Arctic 
Favourite:
Polar Bear - arguably held back from the base game for this very pack to exist, far ahead of the other three species with reindeer a distant second.
Least Favourite:
Arctic Wolf - Least favourite DLC species in general. I’m a fan of having multiple subspecies of more iconic animals like tigers and brown bears where both are more common in captivity, but having a generic grey wolf and then a specific subspecies when we really should’ve had the Arctic Fox instead doesn’t sit great with me.
South America 
Favourite:
Jaguar - Closely followed by the Capuchin and the Giant Anteater but like the Polar Bear this felt like an iconic species that was intentionally held back to be a DLC spotlight.
Least Favourite:
Llama - it’s aged better now it has colour variation and we have more domestics and South American animals, but at the time it felt very disappointing given how few SA species we had and the fact we had no other domestics to go with it either. The other three are still miles ahead though.
Australia 
Favourite:
Southern Cassowary - gorgeous model and fits great with both an Australian and Southeast Asian theme. It’s also another bird!
Least Favourite:
Dingo - from a region of iconic marsupials, a third ‘wolf’ didn’t feel great. It’s aged better now we have received more marsupials, monotremes and birds from the region.
Aquatic 
Favourite:
Giant Otter - honestly all of the animals from this pack have aged fairly poorly for me. All four have a counterpart I prefer more (ASCO, African Penguin, California Sea Lion, Spectacled Caiman) but it’s nice to have diversity and occasionally I’ll use one of these guys instead. Giant otters win out as they’re a species I’ve seen irl and add to South America.
Least Favourite:
King Penguin? - I don’t actively dislike any species in this pack but it’s a toss up between the penguin and the seal. Generally if I ever build for penguins it’s for a small species whereas I’ll sometimes swap out sea lions for the native grey seal as a European so King Penguin gets the least use.
Southeast Asia 
Favourite:
North Sulawesi Babirusa? - Honestly this could be any of the Babirusa, clouded leopard, sun bear, binturong or tapir. I like them all a lot! Babirusa wins simply on how lovely the model is and how nice a surprise its inclusion was.
Least Favourite:
Proboscis Monkey - I love primates but was and still am underwhelmed by this choice. Would’ve preferred a gibbon at the time and now we have two gibbons, I which it was a langur or a Celebes Macaque.
Africa 
Favourite:
Southern White Rhino - the third and final DLC species for me that feels like it was intentionally left off the base roster to be a DLC headliner. An essential species who’s additional was finally a huge relief.
Least Favourite:
Fennec Fox - still love it though, but African Penguins and Meerkats are essential zoo animals.
North America 
Favourite:
California Sea Lion - so iconic and creates new build opportunities. Moose is a close second as such a unique and formidable animal.
Least Favourite:
Arctic Fox - I still like it, but it feels like it sticks out in this pack and really should’ve been in the Arctic Pack. It’s fairly forgettable.
Europe 
Favourite:
European Fallow Deer - an unexpected favourite but an essential zoo animal and great for deer parks. Love it even more now it can be combined with the Red Deer.
Least Favourite:
European Badger - Don’t overly use it as don’t generally consider it a zoo animal. Was more underwhelmed at the time of release but it has grown on me as we’ve received more European species in other packs.
Wetlands 
Favourite:
Capybara - At the point of its inclusion it was my most wanted animal. An essential species closely followed by the ASCO. These two arguably are the most essential zoo animals from the DLCs for realistic builders, alongside maybe the meerkat.
Least Favourite:
Platypus - I can appreciate the uniqueness and deservedness of its inclusion, nonetheless I rarely use it or wish to build for it. It deserves its spot on the roster though definitely as an iconic Australian species.
Conservation 
Favourite:
Scimitar-Horned Oryx - a fan favourite of mine, was on my wishlist and wasn’t 100% convinced it would make the roster so was really chuffed when it made it. But all four species in this pack are some of my favourites in the game.
Least Favourite:
Amur Leopard - draws the short straw as I really like it, but arguably just misses out to the siamang and the wild horse on the basis that they were our first proper horse and first gibbon and so brought really new things.
Twilight 
Favourite:
Raccoon - a great and charismatic common zoo species.
Least Favourite:
Common Wombat - I rarely build for zoos outside Europe and these fall into the obscure Australian species bracket. Would’ve preferred the hairy-nosed wombat of any species and in general doesn’t really fit the theme with the other animals in the pack, feels out of place. Not to mention it’s such a non-descript species, it has no defining features on the surface, a brown herbivorous ball of four small legs and a head. The basic b**** of the DLC roster.
Grasslands 
Favourite:
Emu - another close one as I like a lot of animals in this pack. But to me the emu was the species that was the biggest relief to finally get as it was a long time coming, it’s also another bird. Close runners up include the wallaby and the maned wolf.
Least Favourite:
Nine-Banded Armadillo - simply on the basis that I rarely will use it. Had it been a six-banded I probably would use it a lot but I like to build realistic, primarily European zoos, and these aren’t found here. I can appreciate it still though. I just think six would’ve been better as it’s found in zoos across continents.
Tropical
Favourite:
Red River Hog - this is another close one with three front runners for favourite as all were high on my wishlist, the red river hog is gorgeous however!
Least Favourite:
Asian Water Monitor - underwhelming on announcement. It’s nice to get it and it looks great, but when tropical was announced it was already underwhelming not to be getting a Tropical animal pack given how many species are missing from this biome, and then to not get any South American species either. I wouldn’t have minded this guy so much if Tropical had been a larger animal pack.
Arid
Favourite:
African Crested Porcupine - I’m still a big fan of all the ungulates but this animal is another zoo essential and looks fantastic. I use it a lot in mixed desert exhibits.
Least Favourite:
Sand Cat? - a difficult one for me as unlike most, I actually really enjoy the animals in this pack. I guess the sand cat is the one I’ll use the least and there’s other small cat species I wanted more than this guy like the serval, Pallas cat, European wildcat and ocelot.
Oceania 
Favourite:
Tasmanian Devil - clear favourite for me, although I’m not too fussed by any of the species in this pack. But Tasmanian Devil was a long time coming.
Least Favourite:
Little Penguin - rarely if ever going to use this guy over the other penguins in game. But respect it for what it brings for Oceanian players.
Eurasia 
Favourite:
Mute Swan - I appreciate a lot of the animals in this pack but the mute swan was the most welcome surprise! Looks great, is very unique in the roster in what it brings and another European species.
Least Favourite:
Saiga - This was an animal on the wish list I generally argued against given the rarity in captivity. I actually quite like it now we have it but still not going to argue that it’s a very niche pick and we only get one coat type which makes it even less realistic/versatile. I probably would’ve shoe-horned the blackbuck in instead if we had to have an ungulae given the sloth bear also from India made it in, would’ve maybe made that inclusion feel less oddball too.
Barnyard 
Favourite:
Hill Radnor Sheep? - arguably I like all seven species pretty equally in this pack as they all complement each other and I feel you need all of them for petting zoos. But this sheep is amazing looking.
Least Favourite:
American Standard Donkey - Looks great and very pleased we got a donkey but would’ve maybe preferred a different breed and can see some arguments it should’ve been a pony of some sort.