Topic best race for mage on alliance
For PVP, go human for their escaping racial.
For PVE, Gnomes have a nice intel boost which is great all around for any mage spec (especially arcane, more mana = more powa + arcane is top DPS atm). Worgen have a nice crit boost and a mini-sprint cooldown, which is perfect for fire (Fire uses crit for more DPS). However, for the time being, fire is nerfed to the ground and mages are about to get their own mini sprint.
I'd say gnome for PVE, but to be honest--
--would be the best advice.
For PVE, Gnomes have a nice intel boost
No, Gnomes have a 5% Mana Pool increase. It used to be intellect. a 5% mana increase does not yield more damage. Infact, for arcane it would require you to recover more mana to be at 100% mana for the mastery, which wouldn't help your DPS since the mastery is based on a percentage of your mana, not the actual amount in the pool.