Anyway on a serious note I have always viewed it as Luffy with Zoro at the top followed by Sanji and Jimbei then the rest.
This is sorely based on the way Oda has gone out his way to highlights duo throught the manga and in every generation:
- Roger and Rayleigh (pirate king and dark king)
- Garp and Bogard
- Sengoku and his goat (I am joking)
- WB and Oden (Brothers, when Oden was still on the ship). WB and Marco (After Oden left)
- Shanks and Ben Beckman. (Shanks and Mihawk. You can also view this in the same vein)
- Luffy and Zoro
- Coby and Helmeppo
- Smoker and Tashigi
- Kidd and Killer (Pirate rivals)
- Lucci and Kaku (are now part of cp0)
- Crocodile and Mr
As evident, there are multiple duo that exist in the Op verse. These duo are not just random, they all play a huge role in the influencing the journey of the SH. Even when he makes foes return eg Crocodile, Mr.1 and Lucci, Kaku, he made sure to bring back the 2 members that rivalled Luffy and Zoro. The rest have not received any focus.
Oda has actually never developed an opponent/rival for Sanji throughout the manga like how Luffy and Zoro's rivals/opponents have been developed throught the maga. Sanji neither has a marine nor pirate rival. Only Luffy and Zoro do.
M3 would honestly make sense if Oda actually put in effort to highlight it. If he made rivals for Sanji etc. However, he has never done this throughtout the manga. Sanji's opponents always are only relevant in the arc they appear in then are gone. His rivals also only ever appear in the arc they are relevant to.
Based on manga, the only team up Oda focuses on is the duo that will be rivals for Luffy and Zoro