Edit: There seem to be some confusion about how this event actually works. You aren't voting for "what characters to put in the game", you're voting on what characters will have secondary versions with special outfits in the future, and a larger selection will be featured on some free wallpaper.
That said, they could still use the votes to help gauge character popularity, so by all means vote how you want!
I know I made the right choice for my day 1 pick. Who did you choose so far?