It is hard to compare them since their characters are all such opposites and I really do appreciate both. However, I cannot help but like Marvel heroes better. This is because they are traditionally much more limited in what 'powers' they are given. Such as Superman having dozens of powers compared to Scott Summers who can only shoot lazers out of his eyes.
I personally find that this leaves theme open to much more interesting and creative story lines. It also means that when the bad guys come 'a knockin' there is always that little bit of doubt that your favourite hero/heroine will manage to save the day