Just for fun, let's rank all 15 building themes. You can rank them in a tier list like I did, or feel free to put them in a numerical ranking. Here's my ranking:
S tier: Aquatic, Indonesian, South American
A tier: African, Conservation, East Asian, Europe, New World
B tier: Australia, Classic, Planet Zoo
C tier: Indian
D tier: Arctic, North African
F tier: Twilight
S tier: Aquatic, Indonesian, South American
A tier: African, Conservation, East Asian, Europe, New World
B tier: Australia, Classic, Planet Zoo
C tier: Indian
D tier: Arctic, North African
F tier: Twilight