Until VERY recently, aggro was based on who the mob saw last, they didn't even have to attack. We had Troll fights were some guy just walked by and the troll at 1/2 hp ran over to attack him. Now, it seems to be based on who is doing the most damage but mages can get healing aggro. It also seems like big HP mobs like the Troll have an aggro reset pulse every 30 seconds or so. Right before wipe, I could hold aggro if I got like 3 sold headshots in with my Maul and then had people DPS, then pause for a bit, then go again when I felt I got another few more good headshots in. However, that aggro drop pulrse still remains, but I could get him right back with 1 good whack, then again have dps wait for a few hits before continuing. I play human BTW, so no threat increase but I do like 6-7% more damage than an Oghmir can and beingf tall I can more easily get head attacks in which helps. Due to size + talents I think Thursar would be the best tank for pure threat.