Mario: Really hard to judge for Mario because Paper Mario, Daisy and Cap. Toad are roughly on the same level. Geno probably counts but his chances are about as small as a bacteria and he's technically third party.
DK: Every Kong not named Dixie.(behind K. Rool and Dixie)
Zelda: Groose, Fi, Pig Ganon (likely behind Toon Zelda because muhforbiddenseven)
Kirby: Magolor (behind Bandana Dee)
Pokemon: Too many to count and judge.
Metroid(bets this series won't be even considered): Sylux, Rundas (from a logical, established perspective, behind no one, but Ridley keeps getting voted for and you all know his deal)
Star Fox: Krystal and Slippy (behind Wolf, natch)
Fire Emblem: Tiki, Kamui, Anna(underdogs due to perceived Fire Emblem bias
)
F-Zero: Every character is an underdog, technically.
Kid Icarus: Hades, Medusa and Viridi are most likely on the same level, Viridi is probably higher.
Mother: Underdog series given it's most missed veteran returned.
Animal Crossing: Um...Resetti has a thread. It's something?
Wario: 9-Volt and Mona are probably equal.
Pikmin: Louie has a thread. re: something
Xenoblade: Fiora has had support for a while, but she's being rivalled by Melia and Xross now. [spoiler character that should be really obvious] is probably the underdog despite being in the game already.
Third parties: Listed by company.
SEGA: Hard to tell. Tails is the most commonly cited second newcomer that Sonic/SEGA should have.
Capcom: A third rep is really pushing it since Ryu is in Smash now. Everyone else, I guess.
Bandai Namco: Klonoa has had the biggest support out of all of the Namco reps, so that makes everyone else the underdog.
Konami: Bomberman and Simon are most likely behind Snake.
Others:
Rayman, Shantae, and Banjo Kazooie likely stand above the rest.