This is a question that calls for your own opinion. In the book, Jared Diamond does not pick two of the 14 factors and say that those two are the most important. In fact, he is not even convinced that those 14 factors really are relevant. He says that they do not address ultimate factors at all. Therefore, this question is really just asking which of the 14 factors you personally find most important.
I would argue that the first factor is the only one that is clearly and unambiguously important. This is the life expectancy of people in given societies. It seems clear to me that people who live longer are more likely to have time to invent new technologies. Outside of that, all of the other factors are at least somewhat debatable. If I had to pick one, I would say that it is the second one. It makes sense that places where labor is cheap will not see much benefit in labor-saving devices.
Again, this is only my opinion. Different people can certainly answer this question in different ways.