Khabib is good, but I'd put him under Melendez and Thomson. And I agree with the others saying Diaz should obviously be on this list..
Edit: I'd put Diaz at number 6
HW: Overeem, Arlovski, JDS, Hunt
LHW: Rumble, Rampage, Spong, Gus
MW: Wand, A Silva, Souza
WW: Diaz, Alves, Lawler
LW: Diaz, Guillard, Melendez, Pettis
FW: Aldo, Poirier