best index type for uuid in postgres 11
My primary use case is that I previously had a composite primary key
  and am replacing it with a UUID for easy joins and to not have to
  propagate the primary key's data to other tables.


A hash index wouldn't work for that: it can't enforce uniqueness, therefore it can't be used to support a primary key. As mentioned in the v11 documentation:


  Currently, only B-tree indexes can be declared unique.