Julius > Simon > Christopher > Ralph/Trevor > Juste
>>> Leon > 'Sonia' > Richter > Soleiyu
Julius is and will be the OP. Simon is close second by maybe a millimetre or two. Christopher killed Dracula twice. Trevor was the first one to end Dracula. Juste can do magic stuff.
Leon did not kill Dracula, and he is an asshole towards his descendants. I dunno much about Sonia, but she did kill Dracula (though not the full Dracula). Richter and Soleiyu is weak cause they were controlled by Dracula, but at least Richter ended Dracula once.
This list is Opinion Based. In canon, later they were born, stronger they are.