I'm pretty good at DK. This is my assessment
Slightly brained Ret pala beats DKs 1v1, as well as protret. It's an inherent counter, if Ret is perfectly played DK cannot win. The vast majority of ret/protret do not meet the "slightly brained" criteria.
Great Hunters will beat DKs 1v1 without countergearing etc at max level/gear
Rogues can kill DKs with good RNG and if the DK uses shit poorly, but its 70-30 DK to Rogue advantage
Feral can be challenging if theyre good - if you use expertise gear/weapon you just smash them
Enhance can be tough with bad RNG but very beatable - if you use expertise gear/weapon you just smash them
