What type of data to choose for floor storage?

Question

PostgreSQL

Table of users, you need to store the gender of the person.
Options:
1. Bitfield
2. Boolean
3. Char(1) / Varchar(1)
4. Enum ("m", "f")
Question: what type to choose? Filtering data on this field will be.

Answer 1

If there is a need to make the floor optional, then you can make an enum by adding a value for indefinite (unfilled) there, or use boolean, allowing NULL there.