At this point I would simply advise against making any change until racials for the next expansion are defined.
As far as tanking is concerned, the night elf racial Quickness is the most powerful racial. The expertise bonuses of some races and the base stamina increase of tauren are the next best. Bottom line is nothing can really compare to 2% chance to be missed by physical attacks.
While humans have a far superior usable racial, that is only good in certain situations. When comparing passive bonuses side by side, the Night Elf is the strongest for a tank because no one else can make up that free avoidance exempt of deminishing returns.
Miss also applies to any target, including those behind you. You can also be missed while stuned or otherwise incapacitated.
"In anything, if you want to go from just a beginner to a pro, you need a montage." /w TankSpot WTB Montage for Raiders.