Enha brings extra cc (wind shear and hex), hero/BL, totems, frostbrand, wolves, purge and second char that can heal.
But is squishier than war and have no mortal strike equivalent.
Kill window would be with wolves and BL, rest of the time you will be spamming dispell on the pala, but with grounding and wind shear will have a bit easier time.
DK brings chains of ice, grip, mind freeze, strangulate, AMS and other big deffensive cds, pet can be bonus or liability (extra control complexity vs extra dmg and stun).
Make it belf/tauren and you have additional silence/stun.
Out of all the listed melee DK has the best survivability while your pala is out in CC.
His own arsenal of CCs/silences in addition to palas HoJ/repentance makes this comp proly only one where you can chain CCs to force trinkets/CDs easily instead of relying on burst dmg.