I think Ikaris wins this one,but not by much. U have to look at his thousands of years of battle exprience. There powers a pretty evenly matched
I think that the scope of Cat Atom's powers is significantly greater. He is massively stronger, can fly far faster, can absorb most forms of energy and can affect bigger matter transmutations than Ikaris.
The real only advatages that Ikaris has are his psionic powers and his regeneration.
With the huge power advatage possessed by Capt Atom, I would favour him for the win.