If you're going by the racials, Orcs get the Axe bonus, coming up to a +1% crit chance with both kinds of axes. You also have a +15% resistance to stuns, as well as Blood Fury, which is nifty if you decide to go into "ORC SMASH" mode, but with the 50% reduction to healing for 25 seconds, if may get you into a jam.
If you're playing to be an UB3R L33T PVP SHAMAN~!, then the racials would be a big factor. If you're playing to have fun, I don't think it would make much of a difference, just go with it.
I chose a Tauren for a Shammy but that's only because I was getting annoyed with a lot of the Durotar quests (damn alts).
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"Do you know what "nemesis" means? A righteous infliction of retribution manifested by an appropriate agent. Personified in this case by an 'orrible c*** : me."