Please note that this post is written from a paladin perspective. I neither have a druid nor a warrior :P. Warriors have a bunch of tools at their disposal: stance dancing, disarm, etc...but I don't really feel like listing every little thing. I'm just trying to cover the basics to give a general idea regarding the differences between Bear Druids, Prot Paladins, and Prot Warriors.

Mitigation & Avoidance
Paladin and warrior mitigation/avoidance is almost entirely gear based. In fact, both have the very similar gearing goals, with the exception that paladins need to be somewhat mindful of their spell damage and mana pool. Ideally, warriors and paladins will want 490 defense with 102% block + parry + dodge + miss. Paladins will want around 200 spell damage and around 4,000 to 5,000 mana.

Druids have a significantly higher dodge rating but can't block or parry in bear form, making them unlikely to completely push off crushing blows. Also, because of the lack of leather +def gear, they aren't likely to reach the magical 490+ defense in order to avoid crits. Druids though, have by far the highest HP and AC of any tanking class. They don't try to completely avoid crits and crushes like warriors and paladins, they just take them. For example: At least pre-nerf, many well geared tanking spec'd druids were AT the 75% AC mitigation cap with 20k HP.


Threat Generation
Paladins and druids have scalable threat generation, warriors do not (druids scale with strength/AP, paladins scale with spell damage). Warrior threat, on the other hand is based off of fixed value talents and abilities. It's a trade off: Paladins and druids can control how much threat they generate, but at the cost of stat/gem/gear slots. Though warrior threat is fixed, it's all skill based so they are free to focus on gearing mitigation and stamina.

Paladins can also front load a significant amount of threat because they start off with a full blue rage bar. Avenger's Shield + SoR/JoR + Consecration = thousands of threat in seconds. The fast a tank can generate threat, the faster the DPS can start nuking. On the other hand, paladins LOSE mana while warriors GAIN rage. Even with Spiritual Attunement, a paladin will expend more mana they they will get back.


Multi-Mob Tanking
Warriors can Demo Shout in order to gain initial threat on a group of enemies, but it doesn't generate a significant amount of threat. To my knowledge, they pretty much have to constantly switch targets in order to hold aggro on multiple mobs.

Druids are a little better: Demo roar will generate a small amount of threat (similar to Demo Shout AFAIK) and swipe will generate a significant amount of threat on up to 3 mobs. Any more than 3 and the druid will have to tab switch targets ala warrior tanking.

Paladins are ideal for multi-mob tanking. Righteous Defense will taunt up to 3 mobs off of a friendly target and Consecration will generate around 200 threat per tick for 8 seconds on anything it hits. Also, the more the paladin is being hit, the more Reckoning, Holy Shield, and Redoubt will proc.