GusG:
I could have misunderstood what you were asking. Rereading your several posts in this thread, I get the impression you're asking one thing and I, and a few others, are responding to something else.
Your terms "...greatest sci fi hero.." and 'iconic' hero may appear to be your asking for the most recognizable fictional main character (protagonist) that is easily, readily, and fondly remembered by the shear fact that almost every follower of the sci fi has read and enjoyed the stories (novels, short stories, etc.) involving that character. A popularity contest as to the most well known main character. Hero = Main character.
However, I and a few others, took your question to mean something more along the line of classical college Intro To Western Lit class meaning;
a protagonist who, when faced with a major challenge (physical, mental, social, cultural, religious belief, displeasure of the Gods, and so forth) or a combination of challenges, faces them with the resources available and uses his resources is such a manner to overcome and succeed in his goal regardless of the efforts of his antagonist(s) directed efforts to block the protagonist.
And this fictional protagonist's character is memorable specifically because he / she has overcome the adversarial conflict with wit, humor, quick thinking, physical strength, dedication, stubbornness, mental focus, and none of the Oops, My Bad, or "Dang, Missed it by that much" that mere common people would have.
In short, A fictional character that is intended to be a role model which an individual would want to emulate in his real life. Popularity of reading the story is not involved.
In other words:
In the field of Mystery and Detective writing, Sherlock Homes would qualify as an iconic hero by what I gather is your definition. IMHO, the more iconic hero (my definition) of that field would be the character of Nero Wolf by the author Rex Stout. I suspect few of the general public has any knowledge of the Nero Wolf stories.
In my prior post in this thread, my nominations were to my understanding of you request, not to yours. Sorry.
Phil