The unbiased answer for least authoritative is Chopper. He is the "kid" of the SH crew, the most gullible.
Most authoritative is obviously captain Luffy. Crew is named after his hat FFS
The fact also however is that SHs don't operate based on authority and acts more like a family. Luffy is so unwilling to assert his authority that Zoro needs to remind him he's the captain. But regardless, the point stands that Luffy has the true authority.
There has been some confusions because Luffy doesn't choose to assert his authority, because Luffy ordered by Zoro/Nami occasionally. I too admittedly, was wrong about this earlier. But upon thinking more, it's prety clear - the fact however is that Zoro gets to "order" around Luffy because Luffy lets him. It's ultimately upto Luffy whether he listens to Zoro or not.
When it comes to leadership, it is pretty much clearly implied to be:
Luffy > Zoro > Sanji > rest.
When you see how characters outside the SHs perceive them, Zoro is often confused for the captain, and there have been multiple references to him being the Vice Captain.
It is pretty clear that this is the role Zoro fills within the crew. Vice captain, who checks on Luffy's impulses when his emotions run high. But there is no official position in the crew, because that is the crew dynamics that Oda wants - a close family without strict heirarchy.
When the crew was to split in Sabody, it split into 3 groups - Luffy's, Zoro's and Sanji's. When the crew split again in Dresrossa, Sanji was the unofficial leader of the split crew.
Clearly, Sanji is next in charge after Luffy and Zoro.
Luffy > Zoro > Sanji > rest.
If we want to go a bit further:
Luffy > Zoro > Sanji > Nami > rest
