If you are in defensive stance you can't move, so the main problem is that you can't reach the other opponents.
When you have dispatched of those around you( by cleaving) you can't move to the next group of enemies (the drawback of defensive stance).
It is a better concept to stop the enemies...
Superior Expertise is in Oriental Adventures, Deities & Demigods and Faiths & Pantheons.
Basically it allows you to distribute your full attack bonus to your AC instead of only 5.
Instead of Power Attack I would take Expertise (and Superior Expertise), so you can improve your defensive abilities and I think Cleave is not the best choice for a dwarven defender (because of the lack of mobility).
Remain concsious (nothing sucks more than droping to -1, -2, .... be sure to...