Having spent 5 years studying Islam in 2 Masjids (masjid Ahlu Sunnah, and Masjid Omar Ibn Sayyid), I have been asked to prove why I believe that Islam is false and Christianity is Truth. Here is my reply.
First, the Qur'an and Hadith state that Allah is self sustaining. He needs nothing, and is dependent upon no-one. If this statement, which is made via various Islamic scholars, found in the authorative books of Islam (Qur'an / Sūrah Āl `Imrān: 2 , Sūrah TāHā: 111 etc., and Hadith Muslim: On the authority of Abu Dharr al-Ghifaari ) can be proven false, then one can conclude that Islam itself is false.
To be fair, we will dictate this same statement upon Christianity. The Christian God is self sustaining. He needs nothing, and is dependent upon no-one (Isaiah 40:12-17, 27-31, etc.).
We will propose a hypothetical statement on both Christianity and Islam. By using human logic, we will see which one of these statements holds true.
Hypothetically, if all of Allah's creation was to be removed from existence (Jinn, angels, prophets, mankind, animals, all types of beings, etc.) and it was Allah alone that was left, COULD ALLAH HAVE RELATIONSHIP? Answer; NO! A relationship is to have relations. More than one is required to have relations. Therefore, the most fundamental and important teaching of Islam known as TAWHID (the Oneness of Allah) dictates that Allah would be absolutely DEPENDENT upon His creation to have relationship or community. This is a direct proof of the fallacy of Islam. It's own teachings implode within when they are viewed in light of logic.
Now, from a Christian standpoint;
Hypothetically, if all of God's creation was to be removed from existence (angels, demons, prophets, mankind, animals, and all other types of beings, etc) and God alone was left, COULD GOD HAVE RELATIONSHIP? Answer; YES! A relationship is to have relations. More than one is required to have relations. Therefore, one of the most fundamental and important teaching of Christianity known as the Trinity, or more accurately, the Godhead; Colossians 2:9, (GOD the Father, GOD the Son, and GOD the Holy Spirit) demonstrate direct proof that that God would not need anyone or anything to have a relationship. In fact, He IS relationship. He IS community!
This simple test of logic can easily demonstrate the fallacy of Islam (or any other oneness religion), and the Truth of Christianity on a basic level.
*NOTE* To those Muslims (or others) who will say you can state that Jesus is not God because in the Bible He never said He was (and I beg to differ, but I digress), you to must also them apply the same standard to your Prophet Mohammad as Mohammad NEVER said in the Qur'an that he was a Prophet. So therefore, by your own standards and logic, You are denying the prophet-hood of Mohammad. He cant be one as he never said in the Qur'an that he was one.**