EatChildren
Currently polling second in Australia's federal election (first in the Gold Coast), this feral may one day be your Bogan King.
To answer your question I dont think any character belongs more than another. This isn't some popularity contest. Its not like the most popular kid thats friends with Nintendo belongs to be in. There are different criteria than that.
The only criteria I personally have is that characters who originated and sourced outside of the gaming medium don't have place in Smash due to the tonal differences and consistency of the series so far. If Smash has been anything so far, it's been gaming centric, particularly Japanese gaming centric. I think it would be very odd to include characters that formed outside of that bubble, and it's why I'm happy to see characters like Sonic, Snake, Mega Man, Pac-Man, and whoever make an appearance.