Well I'm a level 22 Gaurdian and I can say that Guardians seem fairly well off. Generally when I have aggro, I HAVE aggro. And nobody can really get it off me. Learn to use "Hold the Line" regularly in multi mob encounters. This ability generates tons of aggro and is reusable every few minutes. It roots you and every succesful it generates hate for the entire encounter. Or something along those lines. When you fight easier 8-10 mob encounters you can see it proc'ing a ton.
The issue I do see is that it's sometimes very hard to pull aggro off the cleric or a beserker or the like, when they have aggro. I've literally AE taunted an encounter 5 times and not pulled them off a cleric when he had aggro. Same with pulling off a berserker who took aggro of an add, I used Anger 5 times and nothing (all I had power for).
Thats the only 1 thing that bugs me. It seems hard as hell to pull aggro off others unless you have alot of power. And the problem is that when it matters the most when the group is out of power and the cleric is getting his [Removed for Content] beat down and you can only taunt as your power comes. And it takes forever to get aggro back. This is what is bad.