OM, Soham, Sivoham, Aham Brahmasmi are Moksha Mantras. They will help you to attain Self-realisation. Om Sri Ramaya Namah, Om Namo Bhagavate Vasudevaya are Saguna Mantras which will enable you to attain Saguna realisation first and then Nirguna realisation in the end.
By Swami Sivananda, from the Book Amrita Gita. Swami Sivananda lived from 1887-1963. He was one of the great Yoga Masters of the 20th Century who made Yoga available to a great public. Copyright of the texts of Swami Sivananda The Divine Life Society Rishikesh