Customer Portal Access with different Customers

Customer Portal Access with different Customers

Hi
i need to share Creator Records with my customers.  The application is somehow a "Task Management". Either the customer (persons)  can create tasks for me, or I create tasks for the Customer.
One customer can have up to three persons, who can access the Portal and work with the tasks.

- customer must not see any records created for another customer
- it should be easy to maintain, if persons at customer change

which approach should i take? 

my ideas

User Field
i create a User Field on every record, where i store (via Workflow) every user who should have access to the record and use this field as a selection criteria in the corresponding report.

Permissions with Profiles
i create individual Profiles for every customer, but then i think i need to create also individual reports for every customer

any idea, how to do this in the best way?
thank you
Lambert