Rebecca
Witch
Shiki
(Happy would've been my third but he's not on the poll?)
Witch - Her intro was the most mysterious and memorable one so far. It was because of her that Edens Zero was revealed to be a ship, and she's the one who basically explained what the plot was going to be. I see her as the main pillar for the ship itself, kind of a mother figure vibe as well. I also like the fact that her name's Witch.
Rebecca - She's basically a nobody who could care a bit more about the world. I think her character is pretty realistic in the sense that she's this person who's been living in the world and knows enough about it to get by, but she's always holed herself up in a room, playing games, b-cubing, and only hanging out with Happy. Suddenly she's about to be plunged into something bigger than she is. So I think there's a lot of potential for her.
Shiki - His personality is just endearing. I think it's because he reminds of little children in class who are always eager to learn, who always look up to the elderly with respect, the total opposite of a bully. The thing is, he's not a little child, so he has to grow up in some way, which I think would also be a development to look forward to.