1.16. Recommendation to recite aloud on condition others are not disturbed

Abu Sa'eed (may Allah be pleased with him) narrated that the Messenger of Allah spent the night in the mosque and heard people reciting aloud. He removed the barrier that separated him from them and said: Lo! Each one of you is privately conversing with his Lord, so do not inflict harm upon one another. Let not some of you raise his voice in recitation over the voices of others. (Related in Abu Dawud. Authenticated by Al-Albaanee)

Reciting aloud is better because it requires more effort, benefits others, repels sleep, stimulates mental activity and so on. Reciting silently is better for the one fearing ostentatiousness. In both cases one must enuniciate the letters and words with tongue and lips, even if audible only to oneself, to receive the reward specified for recitation of the Quran otherwise silent reading for contemplation is still permissable.