Either way, most Mario fans are convinced that Captain Toad is the most deserving character for DLC because he's from a recent title that needs promotion (Plus it's the only thing that would satisfy Toad fans).
There's also Geno, but they might want to talk to Square about that and he's arguably old news. Waluigi is another competitor, but I doubt any AT would get a DLC promotion immediately.
If there's one character that she'll have a hard time competing with, it's none other than Paper Mario thanks to the new 3DS stage prompting more requests with his name. Despite being another Mario, he's from a popular subset of Mario games and got even more moveset potential than all possible Mario reps combined. I did recall that his popularity is huge in sites like Facebook, Twitter, and Reddit (Making him a powerhouse in this ballot).