Shaman in a trio: ogre vs troll?

[iRFNA]

In a trio where the shaman may have to offtank at times, which would be preferable? My friend insists on ogre for the stun immunity, however it doesn't actually protect against spell interrupts from combat, correct? I think troll would be the right choice, since hp regen is basically mana regen for a shaman.

How much does ogre stun immunity really protect against spell interrupts? Does torpor truly make racial regen "obsolete"? I mean, more mana regen is always good, right?