I'll toss in some advice from the warrior side. My main is a 60 warrior. Druid bear tanks work best when you have to (a) hold threat on multiples since you have swipe, and (B) when you are facing something with elemental attack forms, since Druids can get way more HP and the resistance gear is easier to obtain for leather imo. Where you are weaker is against physical single targets, particularly if they fear or aggro dump, and you need to regain threat fast. Warriors deliver superior burst threat, and have better physical mitigation. Healers will often like to heal a bear more though because a crit or crushing blow isn't going to put them in the red zone. Warriors however if they can get base shield block to 25% can via the shield block skill completely avoid crits and crushing blows, which really makes them ideal in many fights.
Creator of the Barbarian variant