At the person who said Mugen and Spike aren't alike: You're wrong.
Spike and Mugen have the same attitude when relaxing (casual/being bored and plain 'cool'), the same attitude when fighting (moving in an erratic way), same attitude when it comes down to showing affection (acting all hostile towards the people they really like), ffs they have a similar hairdue. Even Watanabe himself has said they are very similar.
Spike is indeed Mugen in a different universe.
Watanabe also never confirmed wether or not Spike was dead in the end, so saying that Spike died in the end doesn't make him inferior.
And the most important thing of all: These x vs. y threads always seem to deduce that the one who wins is the one who is a character of the superior anime. Wrong. Strenght of the characters does not reflect the quality of the anime.
The most pathethic Dragonball Z character can take out every single Bebop and Samurai Champloo character just by sneezing on them. Does that make Dragonball Z better then Cowboy Bebop or Samurai Champloo? Hell no.
I say that the fight would be a draw. Same goes for the quality of the animes. Jazz and space-action and Hip-hop and good ole' Japan, I mean, how could you possibly play those out against eachother?