Well, no, racials don't make a large difference at all. The only problem is that WoW is a feedback loop. If the racials are 'overpowered', then that faction wins a little more. Over time, they get better gear and so ROFLstomp the other faction more (on average). Think about it. If I have 10k hp, and I get 5% more, thats 500 more health. Barely a single DoT tick from a warlock, or half an Ice Lance (I think). Just pick what's most aesthetically appealing, unless you REALLY want to win so much