I chose...
mutant animal (stock animal with mutations)...I like the idea of an animal looking more like it is supposed to and then consider the mutations...a talking dog with four partial hands, a prehensile tail, and infra-vision...very cool in my eyes
mutant human (stable mutations)...this is a nudge towards science, Darwinism at it's best, with a lucky few passing on successful genes...the new tribes...tons of potential
mutant plant (symbiotic or parasite)...a favorite of mine actually...the idea of a mutant vine for example with roots tapping into the soft sections of a stock (not mutant) animal or human to gain access to the senses, vocal, manipulation, and movement (I prefer the idea of pure strain animals/plants due to the mutant ones not "tasting" right...perhaps a DNA issue...more so because power gamers cause me much grief, so the idea of "I want plant mutations and more mutations from my host" gives me rash
)
I do also like the idea of vault or dome dwellers coming into the new world as virgins but bringing education/knowledge/tools/etc.
“The most merciful thing in the world, I think, is the inability of the human mind to correlate all its contents. We live on a placid island of ignorance in the midst of black seas of the infinity, and it was not meant that we should voyage far.”
― H.P. Lovecraft