Zanpakuto/Shinigami Rules

Shinigami can be partners with Zanpakuto.
Zanpakuto can be partners with Shinigami,
and can be your commander.
When a Shinigami enters the battlefield,
you may put it's partnered Zanpakuto from
your command zone to the battlefield.
"Which is superior, the Zanpakuto or the Shinigami?"