1. Klitschko 2. Wilder 3. Price 4. Haye 5. Joshua 6. Hellenius 7. Stiverne 8. Povetkin 9. Briggs 10. Ustinov Supposing that Hellenius is healthy, and Haye is active and healthy.
Price's cross is a very hard punch.... But he's too fragile for his power to matter at the top level. He showed that does pack a world level punch against Thompson in their 2nd fight. But I agree. That's the only glimpse of his power at world level, so we can only speculate.
Haye shouldn't count, he hasn't fought in 3 years 4 months. I think Helenius power is overrated, his ko % against low tier fighters isn't particularly impressive. Apart from that fairly good list, I'd go: Wlad Wilder Joshua Stiverne Price (guy hits real hard, just can't take a punch) Parker Povetkin Arreola (even shot) Briggs(even shot) No one else that I can think of among active hw's has truly great one punch power.
1. Klitschko 2. Povetkin 3. Helenius 4. Parker 5. Joshua 6. Mansour 7. Wilder 8. Stiverne 9. Teper 10. Ustinov Parker, and Joshua will likely be higher up on the list as they prove themselves against better opposition. I only ranked contenders, and didn't rank Haye because he's more or less unofficially retired.
I have a problem with the older but not the names. I'd have Wilder at the lower level of that list and Briggs and Stiverne both higher.
I think this makes me working a list together redundant as it's likely to be so close with similar reasoning. Parker and Joshua both have awesome power but they need to fight a slightly higher level to better quantify their current power but against their current opposition they are definitely upsetting people even before they look like they are really dipping into the reserves. I'd not be surprised if either of them deserve higher spots in that list, they've just not proven it yet.
I don't think any HW's power is proven at world level other than Wlad, Povekin, Stiverne and maybe Wilder.