Isn't that basically just syntactic sugar for #1? When you create an enum, it creates entries in a table with numeric values for enumsortorder and a string field for enumlabel. It seems like effectively the same thing.

edit: It is different, as all enum values are rows in the same table and there is a third column to identify which type they belong to. The actual key used to refer to an enum value is not in the table; it's the oid of the table entry. So, I guess retrieving the data from the enum table is technically not a join.