As a non human caster - you can either equip:
403 PvP Trinket with 484 resilience on it + trinket effect
Cunning/Vial/Bone-link with damage stats + proc
Result: 484 resilience, trinket effect, ~500 damage stats, proc damage
Or as a non-human you can equip:
PvP Trinket (above)
PvP On-Use damage buff (no one uses the proc damage one)
Result: ~960 resilience, trinket effect, 2 minute on use damage buff
As a human, you can either equip:
PvP On-Use Damage Buff Trinket - 484 Resilience + 2 minute cooldown
PvP Random damage proc trinket - 484 Resilience + random proc stats you can't rely on for shit
Result: ~960 resilience, trinket effect, 2 minute on use, a secondary proc that has an almost negligible benefit
Or as a human you can equip:
PvP On-Use Damage Buff trinket (above)
Cunning/Vial/Bone-Link
Result: 484 resilience, ~500 primary stat, trinket effect, 2 minute on use damage buff, damage proc
As Undead, you use the same trinkets as non-humans, but can additionally break one 8 second fear or mind control every 2 minutes. Which means you enter fear DR in half the time, which is nothing short of Colossal when you consider that the most common comps over 2200 this season are (as with pretty much all late expansion seasons):
1. RMP - 12% of comps - P bring fear and mind control, these do not affect you
2. RLS - 8% of comps - R bring fear, this does not affect you
4. Shadowplay - 5% of comps - this comp is entirely dependent on fear DRs, their only other spammable CC is mind control, which you are also only half affected by
5. Rsham / Aff lock / Boomkin - 3.5% of comps - extremely dependent on fears
6. Disc / Ret / Unholy - 2.5% of comps - only spammable CC is mind control, ret and dk bring almost no peels and play highly offensive, heavily dependent on priests use of fear and mind control, which hardly affect you
8. MLS - 1.7% of comps - since the mages job revolves around peeling and snaring the melee off the lock and shaman - and setting up all the burst/kills (lock is purely cc and pressure), fear is the primary spammable CC here not Polymorph, which again - as undead - has a fractional impact on you that it does on everyone else because you ignore the full duration fear Every time
9. Disc / MM Hunter / Feral - 1.45% of comps - like knightcleave relies heavily on the priest tanking melee off by their lonesome while the feral and hunter go offensive (albeit the priest gets more peels here than there) - still heavily reliant on good use of fears and mind controls to protect themselves from getting wrecked
So only looking at the top 10 most common comps above 2200 this season, 7 of them rely to greater or less extent on fear and mind control to win games. Undead get to bring two pvp trinkets into arenas over 50% of the fights they face without the penalty of actually having to give up their Cunning/Vial/Bone-Link or their 500 resil/on-use trinket by physically equipping two pvp trinkets.
The ability to have another pvp trinket, is worth a hell of a lot more than the ability to have the 2 minute on-use effect (since the resilience from pvp trinket to on-use trinket cancels out, and you have your choice of secondary trinket regardless as human). What's better, 2k spellpower every 2 minutes for 20 seconds, or two trinket effects?
Will of the Forsaken is easily the strongest racial in the game.