Tonguez
A suffusion of yellow
Great question. I would probably go with the top five, rather than the top three. Five is more dynamic and probably more suitable for diverse world. Three is more focused, and tends to be directionless and comedic.
For the 5e 2024 default, the top five are: Elf, Human, Tiefling, Dwarf, and Dragonborn − in this order.
Since the Elf species is present in this postapocalypse, the default five are probably good enough. Fey Elf, Fiend Tiefling, and perhaps Elemental Dwarf, suggest the cause of the apocalypse is the planar levels of being went awry. Humans and Dragonborns would be the natives of the Material Plane. Perhaps bad behavior among Humans and Dragonborns is what wrecked the planes, causing thoughts, dreams, and reality to bleed into each other.
I'm curious (especially given you have four Human-like races) why you would make Dragonborn native to the material plane alongside humans?