At the risk of sounding bias, I’m torn between Aquatic and Oceania.
Let me explain myself; Oceania is among one of the most diverse scenery packs animal wise, and I know some people are going to be like “really? Two birds and two marsupials?”, but those are both ridiculously broad groups (both broader than artiodactyls or carnivorans) and generalizing them is kind of insane. It’s more like 1 penguin, 1 paleognathe, 1 dasyurid, and 1 macropod. The kiwi and tassie in particular are unlike anything else already in game, the former more so niche-wise and the latter more so in taxonomy.
Aquatic isn’t quite as diverse animal-wise, but the scenery is really what’s making me consider it here. Oceania has some of the more diverse scenery among the other packs, but Aquatic is just on a completely different level than everything else. We’ve had individual pieces that have since surpassed the quality and usability of some of those seen here, but that isn’t the focus and as a set it’s still one of, if not the best pack of scenery in the game. Multiple unique options for rocks, plants, statues, signs, walls, roofs, general zoo props unlike anything we’ve seen since (the murals for example), and a whole bunch of other insanely versatile stuff that almost makes it feel like a mini-base game’s worth of items. And the fact that it’s not tied to any particular theme beyond just “water” or generic zoo props certainly helps. Despite my previous statement I don’t want to downplay its animal diversity either. It’s got two admittedly very unique carnivorans but that’s about all I can think of to put against it for this ranking.
Definitely a very hard one, but I think I’m just barely going to have to give this one to Aquatic. It’s damn close though.