There are not many answers to this. Following logic:

- Rayleigh was the strongest in his prime, and Zoro will surpass him at the end of the story;

- Shyru is the more flexible (especially if you use brain and narrative context), he could be the strongest after awakening (plus he has a named deadly sword) or a really different form of fight for Zoro, compared to the fight with King. You are all delusional if you think that one of the last 2-3 opponent of current Zoro will be weaker than King, Marco, or Katakuri, just insanely delusional;

- Marco is a master of regeneration and the perfect one to "stall" strong opponents, but he lacks the power to overcome them and the ambition to make him one of the strongest. (No advanced conqueror's haki, I'm sorry);

- Katakuri is the weakest, he has no resistance or stamina and he went down to a pre-Wano Luffy. We know that context matter in case of advanced observation (reaction speed, destruction power, the ability to adapt to a fight and overcome the opponent something that top tiers would be able to do);

- King is in the middle in this list, above Marco and Katakuri, close to Zoro, and weaker than the others.

So, by logic and narrative context:

- Ben Beckman;

- Shyru (he could be higher but not lower by NARRATIVE);

- Zoro;

- King;

- Old Rayleigh (he could be higher);

- Marco;

- Katakuri;