That old chestnut...
So we all know that story points represent the 'effort' required by the team to complete a user story (or however you want to word it)... It is, by definition, the collective estimation of the team. Story points equal velocity and all that... So, all members of the team (experienced, junior, etc.) provide their input and come up with their estimate. Using the FS, 1, 3, 5, 8, etc.