They both started the company. They are both billionaires. Paul partially cashed out so Bill is worth twice as much.
In the past 10 years Bill has kept on running the show as his prime interest. He rarely branches off into other things. His foundation is doing wonderful things but other than that he's still the M$ posterboy which makes him the unofficial leader of the free world.
Payl has branched off into whatever tickles his fancy. Museums, Sports Teams, Space Ships etc. (You can see more
here )
If you had to choose which one would you trade places with?