Why I am an Advaitin?
I am an advaitin on logical considerations, although on account of emotional needs I can be a pure dvaitin.
Advaita says that when stripped of their respective attributes, Ishwara and Jiva are both Brahman, which only appears as the Ishwara, the Jiva, and the Jagat (universe). Nature of Brahman is pure knowledge - awareness, existence and bliss. The appearance of difference between Jiva and Ishwara and/or Brahman is on account of ignorance or mAyA, which is eternal, but which can be overcome.
Visistaadvaita agrees that nature of Jiva and Brahman/Ishwara are same but holds that jiva-s are parts of Brahman and are never the same as Brahman. Also, visistadvaita holds that karma is eternal just as advaita that ignorance is eternal.
Dvaita does not agree with advaita and holds that the differences between Brahman and jiva-s are eternal. Dvaita also does not agree with the view of visistaadvaita that jiva-s constitute parts of Brahman, since Brahman is partless -- as per sruti.
When I examine visistadvaita in the light of sruti and Gita, I find two basic problems. Gita says that paramatman (same as parambrahman) appears to be divided in bodies but is one. Second, Gita also says that liberation is knowing that one is not a doer and that atman (soul ) is ever untainted by works. Thus, I cannot agree to the tenets of visistadvaita.
Dvaita tenet is robust and does not appear to contradict many srutis, except the ones that directly say that atman was without a second. But Dvaita interpret it the 'without a second' just as most muslims interpret Allah -- as a seprate entity that is without a second and without any comparison.
But Dvaita Guru has interpreted Mandukya upanishad (it can be read in Dvaita.com). Shri Madhava categorically points out that Turya, which is transcendental Brahman, is distinct from the states of waking, dreaming, and sleeping. He thus proves that Turya and the beings in the states are eternally separate.
But Mandukya upanishad exhorts us to know the Turya. On examination of definition of Turya given in Mandukya upanishad itself, I find that Turya is Atman -- one's own Self, is divisionless, exists without any sense of interior and exterior, and is devoid of works. So, if one has to know the Turya, one cannot be a second to Turya. If one comes to know Turya as separate from oneself and/or as another, the Turya definition is broken and one comes to know something that is not Turya.
Gita also has a similar prescription: that a seeker must know the indivisible paramatman. It is also teaches that the truth is known only in samadhi.
So, logically I follow advaita.
That however should not mean that logic has to be the only reason. If one is more comfortable with dvaita or visistadvaita, logic may be kept aside. But me, I, see no contradiction in following advaita and at the same time to be a theist. Till I am in body or in mind, it iis proper to worship that which is higher than these.