In terms of Human vs. Draenei tanking racials, for Sunwell at least, I would highly recommend selecting a Draenei Warrior over a Human due to the inherent DPS increase coupled with the fact that the hardest hitting boss(es) in Sunwell do not "parry gib". The more DPS you are able to bring to your raid, the more effective your raid will be. This is obviously most prevalent in the DPS-heavy Sunwell instance, but clearly makes sense in other settings.
Overall however, for tanking in Sunwell, I would actually recommend a Night Elf Warrior due to the entire percent of Dodge their racial awards them. 1% of Dodge, as I'm sure everyone is aware, is theoretically 1% less incoming DPS. As, although an extra 60 or 70 DPS (or whatever it is the Draenei's racial will end up maxing out at) can certainly be beneficial in Sunwell, more often than not, your guild will be wiping because your tanks die and not because your DPS is pathetic.