Om is the best name for God

All rishis who go into deep meditation and experience God , hear the sound Om. This is why the Om sound is very important for Hindus. They say that it is the best symbol or name for God. Hindus use the word Om at the start of their prayers and sometimes chant Om when they meditate.

Reference: Primary Hinduism by Seeta Lakhani (Ch.1, 'What Is Hinduism', p.7)