Thanks for posing it in this form - this has been my line of thinking for some time. I agree that it is laudable to weigh other's lives as equal to your own, here.

Personally, though I haven't looked up enough statistics to do the math, my initial approximation says I think supporting charities that fight malaria (etc) is better. My reasoning:

Lives saved now are not just a scalar amount added to the "total number of quality years lived by human beings added across all time" - they are also an investment in the future. Fighting malaria will help speed industrialization (etc) in countries that do not yet contribute as much to research, etc.

In general, most human beings leave a positive impact on society. They invest in their children, perform research, build cities, etc. They give birth to more children, which results in more humans alive when immortality does become reality.