Kuzan or Aokiji is himself a former Marine Admiral. So, it is easy to guess at least he is at par with the rest of the Marine Admirals. He has now joined the Blackbeard Pirates. He is one of the strongest logia type devil fruit users. His devil fruit is known as Hie Hie no Mi which allows him to control and create and even become ice. Kuzan is also likely an awakened Devil Fruit user judging from what he did to Punk Hazard.
7. Charlotte Katakuri
Charlotte Katakuri is one of the three sweet commanders of Big Mom Pirates. He has trained his Observation Haki so much that he is now able to see slightly ahead in future. He is also one of the few known users of awakened devil fruits. He has the power of the devil fruit known as Mochi Mochi no Mi. This fruit allows him to create mochi and even become mochi. He is clearly a special paramecia user as well. He can easily fight on par with an Admiral.