Using Organization is the easiest way for your team to collaborate directly to one GitHub repo.
See "User, Organization and Project Pages".
That allows you to manage a group-owned repository (or repositories).
You can even convert an existing account (user) into an organization.
Note that in all cases (fork or organization), a local clone will be needed for any team member to work on a project.
The question is: what that local clone is cloning? Your initial repo, or one of the multiple forks created by your team members?
Managing one centralized repo is easier.