i find knuckles incredibly fast....the power attack is only useful for solo enemies or early on. later game, with 4 separate procs (stagger, kd, ragdoll, dismember) and a generous splash damage area, you want to be throwing normal attack punches, which are faster than anything except the knife. Their cc is amazing...unless you fight groups with them like you're using a sledge or other melee weapon. For fist fighting, you actually want to sprint into touch range...actually colliding with the zombie. that lets you hit both that zombie and at least 2 clustered behind it.
When i built a fort build, i'd let the first zombie get to a doorway, then charge forward swinging regular attack and it was like a slapstick comedy skit, with all the zombies grabbing their faces and flopping on the floor over and over. I'd take maybe 1 hit per 3-4 zombies in a group, as long as i could keep them all in front of me.
This is on default difficulty btw.
As usual, the calls to buff or nerf melee, yet again, fail to mention what difficulty they're playing on. It won't be possible to have melee weapons performing evenly at lowest and highest difficulty, always walk and always nightmare, and different people play on different settings.