Are metal anchors or buried posts better for 6 x 6 posts for a pavilion?
The pier and footing is the best approach.
A structure, even a deck or pavilion should not have to rely upon the posts being anchored in concrete for structural support. The pavilion itself should be planned and supported to be structurally sound in itself regardless of the type of footing used. If properly installed with an anchored metal post base the posts will be stable and serviceable for many years. Otherwise,with a buried post when the posts rot, which they will, and if the structure isn't sound the only way you will know is if the structure starts to lean - which is not a good plan.