We recently needed to import about 150 users into a fresh WordPress site. To accomplish this we used the Import users from CSV with meta plugin, which worked great! The only tricky part was we are using Advanced Custom Fields for users' companies.
For importing, just adding a "company" column to the CSV turns out to not quite be enough. In order to get the companies to import, an additional "_company" column needs to be created and every row needs to have the same value, field_X, where X is the unique identifier Advanced Custom Fields uses for the field.
This can be found by editing a user from the dashboard and inspecting the input for the custom field. Throw that "field_X" in the "_company" column for every row in the CSV and it'll import the custom field - et voilà!