Bill Gates will be remembered as the man that became the wealthiest in the world by selling Windows.
While Steve Jobs will be remembered for helping re-introduce music listening in a whole new way. Then using his same principles to introduce the iPhone.
In my opinion, I think people will easily forget about Windows as Steve Balmer takes Microsoft down the road less traveled. Bill Gates was an iconic figure in the 90's, but he's not as assertive as Steve Jobs was.
Well, I agree with Andrew's answer to an extent - although lets not forget that Bill Gates is still alive (at time of writing), whilst Steve Jobs has sadly passed away.
And although it could be argued that Steve Jobs was more assertive and more of an 'icon', there's no debating that both these men will go down in history for the revolutionary feats they've both achieved.
I think the answer to this question may come down to the next decade or so... Bill Gates's philanthropic work is well know, and he once said in an interview that the "first part of his life" at the head of Microsoft was a preparation for the "second part of his life" where he is committed to funding research and investing in causes that will have a long lasting social impact.
I think Bill Gates sees the potential good his money is doing now as far more important than securing a legacy. Ironically, if he does end up being the man that helped discover a cure for malaria or something like that, then that could be seen as a pretty impressive legacy in itself!