Both are the only survivors of his planet, came to earth in space capsules as babies and showed powers and abilities beyond the imagination of men.
Both decided to protect the planet that gave them asylum, fighting against any hazards that may threaten the peace of their adopted homes and fought with powerful creatures through the universe trying to preserve what they call justice.
"Action Comics" (the comic book series that marks the debut of Superman) have published more than 800 numbers of the series. Dragon Ball has over 500 chapters for television, besides a great movie gallery. This makes them the two most influential characters in their environment globally.
Curiously the two are closer to the concept of dying and rising again (several times) and are surrounded by clones, children, cousins, enemies, and pets who have their own powers, but are never been able to achieve the same fame.
In this new Century, Hollywood tries to show us what makes these characters so great, but the failure was awesome. "Superman Returns" was the most predictable movie in the history of superheroes movies, and "Dragon Ball: Evolution" was only a poor representation from a parallel universe (parallel but very distant) of the real Dragon ball we all love.