I think 1...Nf6 leads to more familiar openings. If I'm playing black and I feel white is trying to throw me off with a different opening, I'd try to keep the lines similar to what I already know. Nf6 somewhat does that.
Is 1...Nf6 really the best way to defend 1.Nf3?
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Nothing wrong with 1...Nf6. Seems the most flexible while waiting to see how White wants to develop.