I would like to point out the problem with AOE aggro as jugg.
Quick Background: I have a lvl 50 Jugg (with lvl 50 epic tanking mods and gear), and I was once the diehard "Juggs are super easy to tank with," That quickly changed with aoe threat in lvl 50 ops and flashpoints. I have played tanking classes in several different MMOs.
Don't get me wrong, we are mean tanks for bosses and such but AOE we have a few problems and here is why:
We only have two useful AOE abilities, AOE Taunt (30 second cooldown if talented) and Smash. Smash doesn't always grab aggro especially when bounty hunters and inquisitors are Aoeing their face off.
I BELIEVE that one of the main problems is how trash mobs are set up in high end instances. One set of trash mobs (5-8 npcs) is usually spread out into 2-3 small groups. Therefore, they are too far out of reach to be hit by smash. You may say "but thats what charge is for" well yes, but once its on cooldown you are out of luck. Many of the NPCs in these instances are ranged. Therefore, when charge and aoe taunt are on cooldown you spend half the time running around just trying to get into melee, smash, and force scream range of different groups of mobs that you need to gain aggro from. This reduces the amount of time you are actually attacking and tanking targets. Also, one force scream, one smash, etc will not draw aggro immediately from NPCs who have dps spec'd classes AOEin the living crap out of them. Thus, its not as simple as *tab* hit target once *tab*.
I am a diehard tank at heart, but the frustration from the AOE problems with this class has forced me to roll over to PvP (Where i currently smash face).
One additional point:
Even if you disagree with this entire argument. You cannot disagree with the fact that Powertechs simply have a vast majority of AOE abilities that deal both a sizable amount of threat and damage. Also, considering how that most of these AOE abilities require a simple gun shot or missile, the Powertech doesn't have to spend time running around from spread out mob to spread out mob. Therefore 9 times out of 10, the powertech will obliterate a juggernaut tank in AOE threat.
I did not comment about Assassin tanks because I do not have any personal experiences with them nor have I seen one in action. Therefore, I am not quite sure how their mechanics work.