I have to disagree.
Warriors are the worst tanks for most fights unless you have a reason to take one (to the caveat that paladins and druids suck just as badly if you don't have a reason to take one, paladin tanking gruul for example is harder than warrior because we do lack those osht keys for when the dps goes down early)
Paladin and warrior mitigation are similar, unless you need the shield wall / last stand the paladin should tank for the threat gains (if your dps aren't dpsing the difference is probably higher than that of your dps / a warriors dps). Paladins are threat tanks, my threat on single targets is higher than a warriors, and its faster, so unless my lack of osht buttons risks the fight I would rather tank than not.
Druids take more steady damage, if you need to ensure a consistant damage through a fight use a druid, their threat is also higher generally than a warriors. So a fight where its vital to maintain steady damage (say to keep healer mana) it may be better to take more damage consistantly than less damage in spurts. Druids also seem to build the 2nd best threat as OT in rage starvation situation, paladins work better because we can stand in cave ins etc or quaff pots but a druid will generally out threat a warrior as ot.
Where warriors come into their own is progression fights (wtf? what was that, will hit shield wall now thanks), fights with gimmicks (overcharge in TK for example), and fights where there is a sudden massive damage that you know is coming (gruul on large growths etc). Warriors are perhaps not best considered the default tank (which is really who ever you have handy and geared) but the best gimmick tanks. Ok as off roles the other 2 can perform slightly better (healer / off dps - off healer), but if you realistically need the OT in a role other than OT your group is probably undergeared or underperforming anyway, and if your MT bites it picking up the fight as OT in off gear is likely a wipe anyway.
Warriors are not the generic tank unless you are gimping your group, each tank has a place, and each tank has a role, to default that role to a warrior is silly as you miss out on the advantages the other 2 tanking classes bring, every fight is different and every class deserves a shot at fights that are better suited to it.
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Ahh, but you have heard of me.
http://eu.wowarmory.com/character-sheet.xml?r=Lightbringer&n=elyria