Basically, Tweakedirl is 100% right on everything.
For multi-boxing, Guardian is the clear winner. It's such a
set it and forget it tank! Prot Paladin is a clunky clustercuss and, while Warriors are probably the strongest, they need a lot more micromanagement than a Guardian.
Here's my PvE level 20 Guardian Tank for ideas on how to gear up. I decided on 0% Haste because none of your abilities are reduced by Haste and Moonfire is instant cast. Sure, Haste affects your DoT ticks, but after lots of testing it just didn't deliver the same output that a max-Vers/Agility build did.
Agility is important because, like Tweakedirl said, you have almost 100% uptime on Iron Fur—and its effect scales with Agility! I've been toying with sacrificing Vers for a max-Agility set (still running tests) because the healing boost from Vers is kinda dead to Druids.
The problem with self-heals is that you can't heal without leaving Bear form, and leaving Bear Form with 10+ mobs hitting you is almost a guaranteed wipe. With the reliance on a twinked-out Disc priest, you might as well do Agility>Vers, rather than the other way around.
Raw Armor rating is also important because of Bear Form's 220% boost to armor, but unfortunately the Defias set Armor bonus is not affected by Bear Form. That was an expensive experiment
. Losing too much Vers for 8 measly Armor points doesn't seem worth it.