REAVER
1. up to 69% fear resistance (60% reaver + 5% AA + 4% Keep)
2. energy regeneration buff (savage fury)
3. critical rating 15% increase on upheaval/cyclone
4. overpower (hit is 650-750 crit is 1100-1300) with 15 stacks
ZERKER
1. heal boosts at every stack (except 15) so if you have 10k hp it will take 95 seconds for you to fully regen hp with hp stacks alone.
2. 415 natural hp regen = appx 105hp/second
3. dps increase when (a. you get low on hp b. when they get low on hp)
4. armor increase when you get low on hp
Zerker is better for pvp but Reaver is more fun.