Imam Al-Nawawi in his book ‘Al-Tibyan fi Adaab Hamalat Al-Qur’an’ (1/58), attributes the following statement to Al-Ghazali and other scholars:

The differing reports in this regard from the Prophet and the Companions can be combined in that reciting softly is farther removed from ostentation and show off. Hence it is better for someone who is afraid to fall into showing off, to recite softly. However if he is not afraid of that, it is better for him to raise his voice while reciting, because now he will be doing more work and also it will benefit others. If the benefit of doing something extends to others, then it is better than doing something whose benefit remains confined to one’s own self.  Also reciting out loud keeps the heart alert and the thoughts concentrated to ponder over the meanings of what is being read. It also keeps his ears tuned to the Qur’an, makes the sleep go away, makes the reciter more active, besides awakening and invigorating others who were sleeping and unmindful. The scholars said: When one of the intentions is present, then reciting aloud is better, and if the reciter intends to achieve more of these benefits, his reward multiplies (accordingly)