Which character has the superior design? Don't take quality of games into the equation as Rayman obviously wins that.

Sonic

Rayman

Sonic a better designed to be memorable to kids (low detail with a single colour used as a primary indicator of the character), but i think Rayman's design is a lot more interesting to look at, so i'd go with him.

Why such a hard question? They are both 2 of my favourite jump 'n' run characters.

My favourite Sonic design comes from Sonic Adventure 2:

while my favourite Rayman design is from Rayman 3:

I like that they are both a bit cocky in their respective game, but I think I have to go with Rayman on this one. That haircut is just badass.

Rayman

Agreed, I never liked the Rayman design, but the two 2D games are the best in its class. 

I'm going for Sonic. I never liked Rayman's design, it has always bothered me for some reason.

Interesting to note that (as of me updating this) that everyone who votes for Sonic (who commented) has been from NA, while people who pick Rayman are from UK/PAL, where each series tends to perform better in 

Sonic, I think rayman is ugly as hell

Sonic. Rayman's design is pretty lame.

My heavy bias says Sonic.

Sonic, he has the best design and is the best hero! Although I do like Rayman's design too and his games are masterpieces.