Top-down enumeration: Kay, Master X, Duke, Maxie, Vito.
Aaand now I'll explain why I arranged them like that. (By the way, my personal opinion about the characters is here, I don't want to offend anyone).
In one episode, Kay showed envy of Duke and his abilities when Duke passed (I do not know what to call it) energy to save Victor (I do not remember the title of the episode and I am too lazy to look for it). In the season 1 finale, Kay seemed ready to sacrifice Duke in order to gain the power of the Alpha Train carriage, and after that, I can't consider Kay to be "pure goodness."
Although the Master X is an "antagonist," in the Season 2 finale, he tried to help other trains destroy shadow energy. As far as I know, he helped several trains and replaced their engines (but I haven't watched season 2 for a long time, so I might be wrong).
About Duke... I do not know what to say. I'm serious!!! When I was trying to understand Duke's actions and motives, I didn't know what to attribute him to. Like, he doesn't fit the definition of "bad," but I'm not sure if I should classify him as "good." It seems to me that Duke is either "gray" or "balance". What do you think?
There were no special problems with Maxie. I mean, she's like a child! Seriously, it's like she doesn't know what it means to hate or despise someone. And I didn't notice any bad qualities in her. Maxie, I think, is just a kid.
No offense to Vito's fans, but throughout season 1, he literally infuriated me with his appearance on the screen. I don't know, I just never liked him.
Here's a template, if anyone needs it. (I do not claim to be the author of the template.).
