Akuma, Hugo, M.Bison.
I haven't played SF6, but I'd pick Retro M.Bison always.
Very different look, I wonder what his storyline going to be with his new look revealed.
M.Bison (Alpha 3 Final Boss)
Shin Akuma (Capcom VS SNK II)
Garuda (SF: EX 3 + Alpha)
Gill (SF: Third Strike)
Kage (SF:V)
Urien (SF: Third Strike)
Evil Ryu (Marvel VS Capcom)
Seth (SF: IV)
As cool as the rest look, the classic red hair is the go to for me. Shin Akuma's look in Capcom VS SNK 2 is up there too!
Akuma game wise first started showing grew hair in Street Fighter III series, showing that he still has the aging factors of being human. What Shango mentioned is somewhat true, embracing the Dark Hadou does have that benefit of delaying such things. Going off the comics, particularly in Akuma's origin he has always had red hair since childhood.
First Street Fight was playing Street Fighter Collection 2 on PS1.
Top 3 would have to be Akuma, Gouken & Oro for sure & it's debatable.
I was in toss up between Ken & Guile.
Rose is overdue