Both the DKC characters get the vote from me.
Reasoning below.
King K.Rool for Championship because? He's got genuine support, is far more realisable as a fighter, is one of the most unique concepts of a character, has ever lasting popularity despite his very last entry being in a Mario Sport game... It's not hard to see why I choose him. The Kremling Campain, the fact we got a Mii Costume out of ballot popularity, King K.Rool getting a reference in a
Mario game on a street sign... It should all be clear as water that King K.Rool is the obvious choice here.
Ridley has been overhyped ever since the Melee trailer. But guess what, more characters that where not playable in Melee where in the Melee intro trailer
Sakurai has shot the idea down, and you've all been lucky with consistant Metroid appearances where Ridley appears in, so with all things considered... Please step aside.
Dixie Kong also gets my vote over Decidueye. And why? I feel like Decidueye support is heavily forced mostly because he's a new and recent Grass Type starter. His design doesn't stand out too much from the rest, and Incineroar boasts similar popularity whilst not being HALF as forced. Next Grass Type starter of Generation 8 is gonna make people forget about Decidueye within a second.
Dixie has been the star of the last game of the legendary DKC SNES titles. She's one of Nintendo's first playable female heroes, is from a franchise that desperately needs more playable characters. And it SHOULD get more playable characters, because the DKC cast has lots to offer with them. Dixie with her hair grabs and Helicopter Spin makes more than enough for a playable character suited for Smash Bros., and you all know it. At worst she would be a semi-clone, but guess what? Her Helicopter Spin ability alone makes her worthy for inclusion, then there's the hair grabs... She would easily be as unique as Wolf was / is to Fox without even trying much.
Yes both DKC newcomers are big enough names to warrant them being included both. Dixie Kong has recency on her side and is a much beloved main character, and King K.Rool has massive popularity to boot and is in dire need of a new appearance. Decidueye will be forgotten, and Ridley won't EVER be forgotten Smash or not, and is pretty much guranteed for a Boss style appearance anyway.
Nobody can convince me otherwise. This is what must happen.