Where they're from originally, boa's give birth to live young whereas pythons lay eggs, pythons have heat pits whereas boa's don't...etc

Also they look different like comparing a german shepherd to a staffordshire bull terrier I suppose, where both are dogs but different types of dogs. Both constrict around their prey and some boa's can stay around the same size as ball pythons. Some pretty boa's out there too, I like the rainbow boa's if I was ever to get one