ESAM made a good point for this topic,
"If your discussing this you have to discuss what scenario they are battling, because if you are arguing melee fox vs sm4sh bayo, if bayo gets melee mechanics she would destroy fox." -ESAM
This discussion is gonna be *really* hard to actually come to a conclusive awnser.
If you asking who is the best relative to the rest of their roster:
It's Pre-patch Bayo vs Brawl metaknight; since Melee fox has been getting a run for his money for a while now.
Personally i'm going to say Pre-patch Bayo since Metaknight had a lot of tech developed to fight him, while pre-patch bayo just kinda killed everyone with little resistance.