With the new Dungeon Finder, I've found that I really enjoy running the old, low-level instances. There's something pure about a group of lowbie characters facing old-school challenges like Deadmines and Shadowfang Keep in greens and blues. Before talents really make a major difference, where people use the old meat-and-potatoes abilities instead of the fancy-shmancy expansion abilities. Where drops are actual upgrades instead of pure disenchant fodder. Where you enter Wailing Caverns, get lost, and finally finish several hours later, defending a tauren healing a night elf from a giant murloc.
After a couple of runs with dual-wielding or two-handed tanks, I decided to make a warrior and level and gear strictly through the Dungeon Finder. A warrior that, further more, would tank properly with: 1) a shield; and 2) Defensive Stance. The DPS warrior tanks did a lot of damage and didn't really die, but they couldn't hold aggro at all. My rogue kept pulling off them and she doesn't even have any heirloom gear.
So far, my warrior has made it level 19, and I've tanked Ragefire Chasm, Wailing Caverns, and Deadmines.
The thing I've found with low level warrior tanks is that they are really dependent on getting hit once at the start of the fight. Once I get enough Rage to Sunder or Revenge even just one time, the mob is stuck to me, and no one can touch me in threat for the rest of the fight.
However, many DPS like to hit the mob before it hits the tank. That makes it much harder for the warrior to recover and you have to start burning taunts. So far, the main culprits have been paladins. I think it's because Judgement has a slight range on it, and because they have mail armor so they're not scared of the mobs. It's terribly enraging to see a mob running towards me, my finger hovering over the Sunder button, and then see a golden hammer hit the mob's head and "Changed Target" flash on my screen right before the mob reaches me.
Now I truly understand the fuss warriors made over Rage and priest shields. It must have been extremely annoying to them to be shielded right before the start of the fight and not be able to get any Rage at all.
I wonder if the warrior experience would have been slightly better if the "rest level" of Rage had been twenty instead of zero. (It seems appropriate that Warriors get to be slightly angry all the time.) If out of combat, Rage rose or fell to 20 rage. This would give warriors enough rage to use one or two moves at the very start of combat and make them not so dependent on getting hit right off the bat.
That's one of the advantages of Paladins and Death Knights when tanking. Their resource starts at full, so they aren't dependent on getting that initial hit.