Warriors tanking with daggers

I have a little hobby project with a lowbie warrior (currently around lvl 20) who should tank his way through all the classic dungeons.
I'm using the heirloom emblem mace, since that had the most stamina/agi. Only thing is, it is slow (2.80)...
I can get similar stats out of the Wintergrasp heirloom dagger, which is considerably faster, and as I understand it warriors like fast weapons.
I've never really seen any warriors tank with daggers before, so here's where I get unsure.

1. Why would I want to go for faster weapons?
2. Is there any reason to steer clear of daggers as a weapon group?

At your level, no there's no reason, aside for group member perceptions. Once you get Devastate, I believe it's normalized such that you'll be getting AP contributions at the 1.7 speed rate rather than the sword's higher rate. Someone correct me if I'm wrong about the normalization.

1. You can only heroic strike as fast as your weapon swings - slower weapon means less heroic strikes.
2. Typically you're not going to find high-level daggers with defensive stats, and so they tend to be avoided.

Those are the quick answers to your questions - that said, they're both fairly irrelevant to a leveling toon. If you are a capable tank, it is unlikely that you will ever be caught in threat generation, and defensive stats are generally sparse while leveling as well. You will not be crit immune, you will not have high avoidance... typically you'll stack stam, strength, and agi, and deal with everything just fine.