It depends what you want to do and what level you are.
For levelling 1-40, Enhance is great.. then start into the resto tree.
At endgame:
Restoration for Raiding
Elemental for Alterac Valley
Enhance for one on one PvP
But most of all just try them all and find one which suits your playstyle.
Oh and yeah, you should be in the Shammy forums really.