Om is formless but Krsna has got beautiful form, enjoying. And we are addicted to beautiful form. Why something which is not beautiful? Krsna says in the Bhagavad-gita, “I am omkara.” So in one sense omkara and Krsna the same. But I can see Krsna very beautiful and so many things, but I do not see in omkara that thing. Therefore my preference should be to Krsna.
From Srila Prabhupada’s lecture on Srimad-Bhagavatam 5.5.3 — 4 May, 1968