To be REALLY nit picky regarding races, I might argue that;
Troll's are better for "Caster" type shaman (Namely Elem.), due to possible rapid fire LB's via racial haste, and slightly higher INT than Orc or Tau.
Orc are better for PvE, due to higher possible dmg potential due to racial, and axe proficiancy doens't hurt either!
Tauran are better for PvP, due to AoE stun and slightly higher HP.
I use the term "better" loosely, as neither racial really makes or brakes the classes effectiveness. I play a 70 Tauran sham myself. My GF has a Orc Shaman alt, and I have a alt Troll Shaman on a seperate server, of I've toyed around with each race for a shaman class. Frankly, I tend to forget to use my racials typically, and don't really feel like I'm "missing" them when lvling or farming :p In PvP, War Stomp is nice in a pinch, but concidering that it blows a Global CD, and it does have a cast (.5 sec), it doesn't make it a completely full proof "OS" move, but it has its moments. Basically it gives you a "possible" 2 seconds to do "something" (not 3 secs like the tooltip says, since the GCD took 1 sec away, which tends to be just enough time to take a few steps away from your target, or enough time to get off 1 LHW.
Either way, frankly it comes down to look I think, more so that racial traits. Gear offsets any stat difference the races might have in comparison, so IMPO it really doesn't matter!