1 Joshua 2 Fury 3 Wilder 4 Whyte 5 Povetkin 6 Miller 7 Ortiz 8 Parker 9 Pulev 10 Kownacki/Chisora/Breazeale toss up
Miller's background is not boxing and he is still a student in boxing and if he puts the effort in practice I'd assume he has even more potential to improve than all the other top guys.
Vitali was a better kickboxer also even though he got knocked out in one his kickboxing matches by a fighter who also became a boxer, Pele Reid.
The order of rank will vary but I think most lists have the same 10 names 1. AJ 2. Fury 3. Wilder 4. Povetkin 5. Whyte 6. Pulev 7. Ortiz 8. Miller 9. Parker 10. Kownacki