A lesson in Aggro-----
Aggro is not somehting you want to share evenly. In WoW there are healers, tanks, damage dealers, and pullers.
Pullers have stealth or ranged attacks (Hunters, Mages, Rogues mainly). They also usually have lower armor but do more damage (dps). Hunters are the exception to this, they have a pet that usually has decent armor and they can armor up pretty well. Rogues need to be nerfed. Their job as the puller is to get the monster out of range of the aid of other monsters so no one pulls those monsters aggro.
Damage Dealers are just high DPS. Mages or Warlocks are probably the 2 biggest classes for this. Go ahead and argue with me. They hardly ever have enough armor to survive more than a few seconds in melee.
Tanks have extreme amounts of armor. Hence the name- tank. They dont do a whole lot of damage but do enough to keep the aggro so no one else gets it. They have moves where they make the monsters angry. This is 99% of the time a Warrior class.
Healers do decent damage and have next to no armor- but can put up a force field around them and heal themselves as well as others. Paladin, Shaman, or Priests, Priests can also ressurect a fallen comrade.
You have your group, they walk up to a room. The tank gets in front. The puller right behind him. DPS out a little ways. Healer in teh back. Puller hits the monster with an attack, monster runs in to attack puller- tank starts wailing away on the monster and the monster gets pissed at it. dps start in blasting away at him. Healer basically stands back and heals anyone that is getting hurt bad. If the healer rocks out wayy too hard the monster runs at him. It is the tanks job to get that aggro back, but anyone that gets the aggro off that healer is a hero- unless its a dps class- they just die. But thats okay the healer can res(surect) them after the battle.
That sums up aggro and battle.