I can't speak for other druids but I've tried both catform/cower and bear form when I do manage to pull aggro.

In my experience, catform/cower = dead kitty far, far more often than bearform = dead bear.

Since the frenzied regeneration option was added to bear abilities this is even more true.. the tank may need to work harder at regaining aggro but at least I've survived the encounter to go back to healing once the tank has taken the mob back. The reason the tank gets aggro back with catform/cower is normally because I'm dead.

When I do any significant changes to my gear, I tend to retest this and I've yet to come up with a combination that would make me lean towards the catform/cower method. It is simply not anywhere near as effective as the priest fade ability at reducing aggro.

It could be that my bear form is sturdier than yours (while tempted by some cloth stats, I've yet to be tempted enough to give up leather for cloth) or that my heals generated more aggro but the catform/cower method just isn't effective enough for me to trust my life and the lives of my raiding companions to it.