I think Cody should win the Men's Rumble.
Cody seems the obvious choice if he's healthy, which it seems he will be. And, a lot of times the obvious choice is the right one. If not Cody, Zayn winning could be interesting, especially if you have the Bloodline turn on him before then. That could be literally the biggest pop in Mania history if it's done right.
Charlotte winning is always a possibility... cause Charlotte wins a lot of stuff. To be fair, she's very talented, but she's another person where she keeps being given moments she doesn't need. She didn't need to end Asuka's streak or beat Rhea for the NXT title. Charlotte is about as over as she will be I think. I don't see her vs Bianca being a match people are dying to see, and I don't think anyone really needs to see Charlotte vs Rousey again. (Although, lets be honest and give Charlotte some huge props, cause she had some great matches with Rousey, and others haven't been able to do the same thing).
The women's rumble is a lot more interesting to me because they have two belts, so there's more directions they could go, especially because they have a really dominant face and heel holding either titles. Rhea Ripley I think is the best choice. Becky could also win to set up a match with Rousey, although you could just book that match without a Rumble win. If Banks came back I'd be down for Banks vs Belair II.