Its not so simple; stamina > all until you can surive any burst from a particular enemy, after that, is where the 'debate' begins.
[Tank] Equilibrium Point Between Avoidance and Stam for a quick rundown, also on the second page of this forum is a threat per second thread.
in all honesty tanking as been set up more as an art than a science, since the specific values "required" change depending on the boss fight and how many hits it takes to kill you.