I have all 3 tanks barbs are by far the worst at threat. The reason why is because you have to enrange to speed up attacks to hold threat but then have no stamina to block big hits in TIC. So either enrange all the time to hold threat or die to every big hit.
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As for Fighter tank, I've never had issues with holding aggro in IC. The encounters I use are Enforced threat (adds 10k combat adv to me), Linebreaker and shield throw (with feat). Don't forget you have tab for retaliation, with feat its another up to 600 magnitude taunt you can use every 10 seconds.
Pally has no issue holding aggro if you know what you're using; I use Bane, Sacred weapon and Templar's wrath. Bane is only used when feat baneful strikes is proc'ed, it's job is to proc the feat for divinity regen anytime you attack for 10 seconds. Sacred weapon is obvious, templar's because it has increased threat, smite doesn't its a hard taunt.