I don't wanna rank Jo2uke until Part 8 is over, so I'm leaving him out.
Johnathan. I like him, but as a main character, compared to the others, he just doesn't have that special something that makes him really compelling. That's why he's on the bottom.
Giorno. Kinda towards the bottom because he just doesn't grab me like other JoJo's, but he does have some awesome development, and I especially like him the most towards the end of Vento Aurero.
THIS IS WHERE IT GETS HARD FOR ME, JFC
Jotaro. It literally pains me to put him this far down, but it does NOT mean I don't like him or anything (Hell, the same thing goes for Giorno and Johnathan, I love them too), but as far as character development goes, I just... can't really think of anything. I love him, and he develops a bit in Part 4 and Part 6 but in Part 3...? He doesn't do too much except beat people up and complain. Not that that's a bad thing, but I think that's why he ended up at 5.
Johnny. This is the part of the list where I just have to decide who I love MORE, and Johnny ends up at 4 I guess. I love Part 7, and Johnny is an amazing character. Gotta love/hate that ending, too :'(
Joseph. I mean... It's Joseph. The way that he out thinks his enemies instead of overpowering them is just really appealing to read/watch. Not to mention that quick wit and awesome clacker ballweapons. He's just the full package you want in a main character
Josuke. He has the most badass Stand of all-time, and holy shit, ya better not talk smack about that awesome hair. He just has some of the coolest moments in the series and after reading Part 4, he feels like a pal.
Jolyne. Maybe not the most popular choice, but I think her character and development throughout Stone Ocean is the greatest in all of mange, let alone just JBA. She cool, she's quick-witted, she has an interesting personality, and she has one of my favorite Stands (second only to Crazy Diamond). All in all, she just has to be my fav.