I believe the warrior should always pull. No exception. I keep seeing posts and even game guides that believe a hunter or rogue should pull then the tank should magicly grab aggro. A warrior needs rage to grab aggro fast. Without it he has to attack and be attacked to build rage to use aggro generating abilities. When a hunter pulls the warrior has little to no rage potentially built up to pull aggro off the hunter or rogue. It's harder for a warrior to grab aggro off someone else. Next there's the idea that a warrior or rogue can fein or dissappear if a bad pull happens. They can for sure. But what happens if it is resisted? Also in the rare case of a bad pull the rest of the group can retreat and not attack the mobs letting the warrior grab aggro and die. Let me know what you think and if I'm off base on this.
I normally pull in instances but I don't have a problem with other people pulling. I will often let a good Hunter pull since it enables them to time their pull in relation to their trap cool-down. We sometimes use Mind-control as a pull in order to get mobs to kill off the MC target first. We don't use the sheep-pull much but I can work off of that if necessary.
I like to do the pull if I'm going to be tanking more than one of the mobs but even that isn't totally necessary. I was playing OT to another Warrior in a 5-man the other night and he would pull and I would just grab my two OT targets out of the group by hitting one with ranged as they ran towards the MT and then smacking the other with an auto-attack and no rage was used at all. Also remember that Taunt has no rage cost at all so it can be used if necessary as well to gain snap aggro on a target.
The easiest way to tank a pull is to pull it yourself but it is not the only way that it can be done. The 'best' way is the way that gets the job done without anyone dying (or a minimum of deaths in the case of some really tough pulls).
Oh - and I usually pop Bloodrage before every pull and that gives me enough Rage to toss a Shield Slam or Thunderclap right off. There is no real reason to start a pull with no rage at all.