This is a very intelligent question and one that is difficult to answer, because Africa is an enormous continent with many different countries. Moreover, it is not possible to quantify such a question. With that said, we can make an educated hypothesis. Here are a few points that favor geography as the more important factor of influence.
First, Islam has not spread all throughout Africa. For this reason, we can say that the influence of Islam is somewhat limited. The most populated Muslim countries are mostly in Asia. When it comes to geographic limitations or advantages, there is no country that is exempt. Countries have to deal with whatever land they possess.
Second, according to the newest statistics, there might be more Christians in Africa than Muslims. If this is the case, from a religious point of view, Africa is impacted by Christians as much as Muslims.
Finally, for the vast history of the world, people could do nothing about their geographic limitations. Even now with all our modern technology little can be done. So, by all account is appears that the geography of a land with whatever natural resources it possesses plays the most important role.