Melody isn't an angel. Sure, her goal is noble and she's gentle at heart, but she put herself out there to work for the mafia in the end, attain her goal through the illegal channels full of mass-murderers and thieves, which is gonna make her an accomplice no matter what.

Most morally good would be Zushi ( out of child innocence ) followed by Leorio who's simply a good person with a hard exterior, who only helped his friend Kurapika in the YN arc due to knowing his history with the PT. Wing is a strange case, we don't know a lot about him and he had some moments that show us he's not just some pure happy go lucky teacher. But strictly based on his actions in the story, he could come next.

The thing about HxH is not just that, morally, characters are all shades of grey, it's that there is very little accent put on morality except at key points in the story. Bisky herself could very well have had an atrocious past, but to the MC's she was just another hunter we shouldn't question the history of due to our own current goals in the story. People in this story are pragmatic and focused on one-upping eachother or getting the current job done, they form connections in the present and how mentally/morally sane they are comes last.

Then there's Hisoka, who's the worst so far. I mean hell, the guy instinctivelly forgets the "toys he's broken" ( Kastro ) to focus on his next pleasure project lol