I would suggest an arguement that in terms of "True A List" characters, Marvel only has the following (and I would argue they are A List in this order): Spider Man, Wolverine, and The Hulk (DC only has two true A Listers: Superman and Batman).
Marvel distances themselves with a plethara of B List characters (frankly too many to list) including the Fantastic Four, most of the other X-Men, most of the other Avengers (I would dare say Captain America is a past A Lister), silver surfer, etc. DC truely only has those characters that are in the Justice League as B Listers (Green Lantern, Wondern Women, etc.).
By the way, my definition of A Lister is someone who can sell there own comics, in large and steady numbers, toss out blockbuster movies or television, and be recognized world wide as an iconic character. I agree that Iron Man is surging in popularity and may reach that level (he is probably closest of the B Listers.