Hey, so, I've been on the long and arduous journey of reading One Piece. And no, I'm not crazy, it's just fun to do something stupid, yet challenging sometimes.
I made it far enough into the series to where I feel comfortable enough ranking all the main characters, albeit before the Timeskip. I do plan to do another ranking once the series ends in order to compare and contrast, assuming that I'm still alive at that point.
Oh! And tell me who your favourite is, I'd love to hear your opinion.
9th Place: Brook

I feel like Brook got the ass end of the deal, joining in Thriller Bark and then immediately getting wrecked in Sabaody Archipelago not soon after. His introduction is actually pretty strong, and I loved his backstory with Laboon. His design is also fucking sick, I was big into skeletons growing up, so as a kid I would've been all over him.
I have two major problems. The first is that he's not funny, he's just stupid. I really don't like this copy-paste style of shonen anime humour, with the panties and the nosebleeds, I'm so sick of it. He's also got skeleton jokes, fart jokes, it's all super lame to me.
The second is that, I feel like he doesn't differentiate himself enough. It makes sense, he's the musician, it's his job to keep morale high, so he needs to relate to each Straw Hat. But that's never been my favourite, I prefer it when a character can feel specialized in their own right.
8th Place: Sanji

Dear god, how the mighty have fallen. To start things off positive, Sanji's fighting style is visually distinct and I don't think any of his fights have felt disappointing in any way... And that's it, that's the one thing Sanji has over Brook.
As a character, he's like the Lisa Simpson to Usopp's Bart Simpson, if that makes any sense.
Sanji's isn't a story about growing as a person necessarily, but rather coming to terms with who he already is and the codes of honour that he lives by, both as a chef and as a man.
The problem comes back to that copy-paste shonen anime humour again. Now Sanji's entire personality is that he likes hot girls, panties and the nosebleeds, etc. He's just very unbalanced as a character, leaning way too hard into the same joke over and over.
7th Place: Luffy

I wasn't expecting Luffy to rank very high, simply because he gets absolutely zero development. Luffy is stupid, he's stupid and hungry, and then he fights. This results in a very fun character, sure, but also one that's very simple.
I think it was Long Ring Long Land where it hit me, that Luffy hadn't proved himself to be a very good Captain yet, that problems were still being caused by Luffy not taking things seriously enough or caring about the consequences.
The big thing I wanna see from Luffy going into the post-Timeskip is, I wanna see Luffy mature a little, and get to see him grow past just being stupid and hungry.
6th Place: Franky

I can assume that Franky was an acquired taste at first, but for me, one that I was totally on board with. He's essentially like a divorced father and that's perfect for a series like One Piece.
Franky actually does feel balanced, where he can be really silly like all the others, but he also takes things seriously, and he's hot-blooded and can put up a fight.
He's also all around a very caring and compassionate guy, he cares for others so much and will cry just because he feels for them.
So, overall, I'm completely on board with Franky, and I can even see him going up on the list so long as he's given more interesting things to do.
5th Place: Tony Tony Chopper

I am shocked that Chopper ended up ranking this high, but here we are. Chopper has one of the most tragic flashbacks, sure, but what actually ranks him so high is his constant evolution and development.
He proved himself useful in Skypeia, is willing to forego himself to become a monster in Enies Lobby, and after Thriller Bark there was a sense that Chopper had really grown into a brave and strong character by this point.
There's just so much to Chopper that I wasn't expecting, even if he appears as a cute little mascot on the surface.
4th Place: Nami

Nami was the most difficult to rank because she was my favourite at the top of the series, with her emotional climax acting as the crux for the entire East Blue Saga.
She then goes on to grow as a character, culminating in acquiring the Clima-Tact in Alabasta, and her sheer drive to save Robin in Enies Lobby.
The reason she gets bumped down a bit is in Thriller Bark, where I feel like she mostly got treated like a pinup and a damsel in distress, and doesn't really come back into her own again until the final battle.
The biggest thing I'm interested in, is to see how her abilities develop. I've never seen a power quite like this in anything ever, so it's always exciting to see her use the Clima-Tact.
3rd Place: Zoro

The big vibes that I get with Zoro's fanbase is that when they were in middle school, they probably thought they were too cool for the silly rubber boy, so that's where Zoro comes in to pick up the slack.
The reason he gets ranked above Nami is that Zoro manages to be consistently good throughout, he's given a lot to do and there's always a good sense of progression with him.
His humour also meshes very well with him, he's kind of a meat head, and he gets lost all the time. It feels way more organic to him as a character, rather than just a set of standard stock anime jokes.
Zoro is just incredibly solid. He doesn't quite reach Top Tier for me because the Tashigi stuff, pfft, whatever. If he wants to reach Top Tier then something major needs to pay off for him, but I would be shocked if Zoro dropped down in rank regardless.
2nd Place: Usopp

Usopp was my biggest surprise going into this series. Usopp is supposed to be like you, the audience, the one who's the most relatable in terms of his feelings of inadequacy. Usopp is the everyman who has to grow the most, and as such, Usopp feels more like a main character than the actual main character.
I felt that Usopp was pretty well established in Syrup Village, same with Little Garden, but then after Water 7, Usopp becomes the best character in the entirety of One Piece.
His cowardly fights were always my favourite, even all the way to Thriller Bark, they were so much fun, and you're always rooting for Usopp.
1st Place: Nico Robin

You know that feeling after you've escaped your 20's, having finally overcome your long battle with depression? That's how Robin feels to me. Robin felt incredibly validating, especially as someone around my age that I can identify with.
I loved her dry and dark sense of humour. She has weird tastes sometimes and she likes "cute" things, having a childlike imagination. And these are all things you can relate to if you were a trauma baby yourself.
I thought her whole backstory was the absolute best, and overall, in the forefront of my mind Robin *is* One Piece to me.