I am going to attempt to rank the characters.
Luffy > Zoro > Sanji > Brook > Usopp > Franky > Chopper > Robin > Nami
Luffy
While swordsmen are usually my favorite types of characters, Luffy is just too awesome not to be everyone's favorite. One of the absolute best lead characters in any anime or anything ever.
Zoro
As I said, swordsmen are usually my favorites. Zoro is one of the coolest and most badass swordsmen ever. Even more badass now with the scarred eye.
Sanji
The monster trio is of course the best part of the Strawhat crew. All three of them are exceptionally awesome. Sanji is a cook that only uses his legs to fight, and it's always a blast to watch his kick techniques. His rivalry with Zoro is always amusing too.
Brook
If you had asked me only a few days ago, I'm not sure Brook would be as high as he is now. I don't know what it is, but I just suddenly started loving him way more than I used to. He's just so hilarious, and his voice is wonderful. His entrance in Thriller Bark to save Robin and Franky from the spider was amazing ). Yo-hohohooo, yo-hohohoooo. So good.
Usopp
He used to be the most cowardly of the bunch, but always acted more manly than he was, because he dreamed of being as manly as he pretended. Now he is manly. I've always liked him, but it's hard to deny that he got much better when he invented his Sogeking personality. He's a great source of comedy in the series, but the amount that he's grown is probably the biggest of all the Strawhats (unless you include boobs).
Franky
He's the only one I liked more pre-timeskip. Still, he's a great character. He's an older and more experienced member of the crew (along with Robin), has a lot of knowledge and knows how to keep calm when others are freaking out (mainly Usopp and Chopper). He's also the reason the Strawhats have one of the best pirate ships in the world.
Chopper
He's the dumbest next to Luffy, but only when it comes to common sense. He has a valid excuse for that at least, since he's not actually human, so he doesn't necessarily understand human traits. Like he can't always tell them apart or recognize lie from truth. Sometimes it gets annoying, but not often. It's usually amusing in some way. Regardless of that, he's an excellent doctor, and even though he's always the first to get scared along with Usopp, he shows tremendous courage and ability when the time calls for it.
Robin
When she first joined the crew, I thought it was awesome because it was unexpected and she seemed really powerful (at the time). Then while everyone else was growing and changing, she stayed the same. She was kinda boring. Until Enies Lobby, when she finally had her big character development time, and she got a whole lot better. And I think she's gotten even better still, she's really found her place among the crew and even has a unique sense of humor that I find very refreshing. She's also the most calm and collected member for the most part.
Nami
One of the longest running characters of the series, she was pretty much there from the beginning. She's grown exponentially in both character and boobs. I don't consider the latter as important as the former. Boobs are nice, but there is such a thing as too big. Now she feels the need to only wear a bikini top, which I find silly. Especially with Sanji losing a ridiculous amount of blood every time he looks at her, you'd think she'd be decent enough to cover up a little more so as not to kill her crew mate. Honestly she's a great character but the weakest of the bunch, I don't have as many good things to say about her as I do the rest.
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~Halo Everybody run!
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