I'm taking iconic to mean whatever version I think of when I think of what a character looks like. If i think of Iron man, I don't think of Heck's version, or Kirby's version despite their influences on IM's creation and design. I think of Gene Colan's work, but these are questions with no real answer (except maybe Kirby on Darkseid for DC or Steranko on Nick Fury of SHIELD).
And as for Black Widow, John Romita Sr.. was the first to draw jumpsuit 'Tasha in ASM 86.
But these are all ideas and opinions. I'm open to any differing choices, even if I'm gritting my teeth and mumbling "are you ^&%$ing kidding me?"