(Goblins are pretty good, also you can use your goblin rockets while Dispersed)
But overall I'd go with Troll for PvE and Undead for PvP.
Undead. Always undead..
Troll for fights like Ultraxion or Spine, Goblin where movement is a factor.
Undead because we have devouring plague (3 min CD) and touch of weakness. Touch of weakness proccing blackout is really pro for arenas.
If you think you will be on heroic spine encounter someday then take troll, otherwise goblin.
Tanking is a job, doing dps is a science and healing is an art.
Oh my. I had totally forgotten about those racials.
Hex of weakness was a castable debuff (curse), which reduced attacking damage by some insignificant margin, and added a healing debuff. Was pretty neat in PVP, since you could chaincast the lvl 1 version of the spell on virtually anyone for some hefty healing debuff spread. It was utterly useless in PVE.
Touch of weakness was a self-buff. If someone hit you with a melee weapon, they would take roughly two digits worth of damage (which was silly low even in TBC), and suffer a similarly insignificant melee damage reduction. When hit, the buff vanished. The only real use this spell had in the game was as a "dispel buffer" - since dispel would remove a random magical effect, you could get lucky and it eating this worthless thing instead of a real buff. Actually... thinking about it, I think shadowpriests could use it to proc "blackout", which was a random stun chance when doing shadow damage. It was very random indeed, but often spelled the difference between "rogue murdering you in one stunlock" and "being able to run away". If you were shadow that is. PVE Holypriests like me would have gladly swapped it for confetti explosion.
Consume Magic was another of those worthless priest spells. Unlike devouring plague, chastise, symbol of hope (instant version of hymn of hope), fear ward or shadowguard - all which were actually pretty neat; consume magic dispelled a random buff from yourself, and you gained 100 mana for the effort. Which was somewheere between slightly and significantly less than you needed to re-cast said buff, and barely enough to cast a rank 4 GHeal (the TBC equivalent of Heal). The only reason this spell was kept around was that Human priests had it worse. Feedback was so bad that you immediately lost at anything you were doing simply by casting the spell.
Ah, memories. The game sure has gotten better, I must admit.
I was doing some dba work (after my post) when my memory came back to me and I jumped on to alter my post but I've been called on it already. Yes I remember that touch of weakness spell now which was like a single use shadowguard with an added effect. Personally I prefered shadowguard and Hex of Weakness.