The eggman name is just an insult sonic gave robotnick in sonic adventure 1 that became a popular name, even among sonic team.
I go with sonic, especially in a one on one fight with mario, besaides I find that sonic game's have a better story line to them (most of the time) mario is just the classic rescue-a-princess-from-a-dragon type scenario, mario saves one princess, and occasionally... wait has he ever saved the world? just about everytime sonic gets into action its a world saving event, not that I don't like mario, I like him too, I just like sonic better.