I think it's better if we take charity work with some pinch of salt. Because no matter how you look at charity activities these days, it comes with some price.
Coca-Cola and Pepsi are into charity as well (atleast here in india) but at the same time they are mining tons of water, destroying environment with plastic and yes, there are cases of excessive pesticides in coke and pepsi.
Many big corps and celebs do the charity work (not out of goodness of their heart atleast not all the time) for keeping fame and the money. Anjelina jolie is an exception to that for taking kids at home, but it's rare to see such folks. Charity is so hyped that if you're a celeb and have no charity work then you're considered as next lindsay lohan or britney.
Here in india there are plenty of missionaries working under the title of charity, aim behind that is religious conversion. Any non-religious person can see this coming as there is a lot of deceptive history of missionary charity. If you're a catholic and religious, you'll find it in no wrong taste but looking at the political and the educational abuse side of it, religious charity always has deceptive purpose. As religion is the only thing in this world that can go inside politics and education (includes science) and social structure without much resistance. Take case of this hindu temple
, the daily turnover of this temple is in 7-8 figures, it'll be foolish to call this country 3rd world if you spot 5-6 temples or church like that in each state. This temple also has access to politicians and educational system such that it's not hard for them to get religious input inside education or social or political structure. In kerala state (india) there is charity work going for families to give birth to more than 2 kids and get 10k INR (250 US $) per child for financial support(one-time). In reality 10k hardly cover expenses of any family for few months. That aside, this increases the number of Catholics in that region and it becomes easy for them to manipulate state laws, education and business respectively. Mother Teresa ? she's just another person who is contributing to this. Some choose to critic religious charity, some choose to go with the positive side, but i choose to look for the bigger view of religious charity. I can only imagine what these religious charities can do to countries which are damn poor to defend or feed their countrymen. I'm sure they take advantage during natural disasters (haiti, tsunami) for their conversion stuff in the name of good. You see, religious charity always comes with some cost, they're no different than business charity.
Now coming back to topic with bill gates, i have respect for him because he's considering charity work for research and awareness in some of the diseases that includes cancer, AIDS and few others. But what makes me go back to skeptical mode with him is that, if he's done with the business stuff in life, why he's bothering with "robin hood tax theory" in G20 Summit?
Media is so cheap these days that they make charity work as a cool lifestyle. Charity isn't something that is pressworthy or fameworthy, it should come from the inside, if you're into humanism. On that point, be it bill gates or buffet, it's waste of time to rate them over SJ. Atleast SJ didn't took part in charity work for deceptive reasons.