^Basically, this.Vegeta tells a story of true change and dealing with pride and failure and Goku is great as well for his eternally positive attitude and heartfelt desire to see the best in people and show mercy.
IMO Goku is the best example of what truly being powerful means, to be merciful relaxed/childlike, and kind, all while trying to improve others around you so you can get an even greater challenge. Vegeta shows exactly what happens when one is boisterous, prideful, and self absorbed when they attain power. At first talking shit and being the best is intoxicating and seems cool but eventually that kind of person is humbled and ashamed of what they were.
Both are prime examples of a principle we all should incorporate - to never be satisfied but instead always striving to improve ourselves, even if that means suffering to attain that new level of self improvement.
But in the end Goku is the best because he embodies what real power is, the power to protect, to help others, and be kind. Vegeta himself realizes this is the truth, hence why he changes in the end.
Being an ass when one is powerful is easy but being kind when one attains power is hard. Nothing good ever comes easy.
These two characters are basically what inspired me to become a storyteller, so I've spent a lot of time breaking them down both on a charismatic/entertainment level as well as a symbolic/philosophical level. DBZ is so good at canon-raping itself and has some of the cheesiest writing you can find, even for an anime dub. But in the end, it's the brilliance and charm of the characters that allow me to look past all that and enjoy the series greatly. These two characters basically carry the show, and in the end I'd hate to decide. Both have been (and still are) role models in my life, and I would hate to see DB without either one.
As far as the vote goes, there is only one, true champ...
Mr. Satan! Yeah; ahahahahahahaha!