I'm fine.

I'm good.

It's fine.

It's good.
"fine" or "good," which is more desirable to describe one's state?

How are you?

(1) I'm fine. (2) I'm good.
Which describes his better condition or feeling?
Both are social gestures and synonymous. It is best to mix them for variety's sake-- along with OK, just fine, doing all right, smokin', etc.
I think if you want to describe your health
I'm well.
would be best.

"Feel well" - "be in good health."
"Feel good" - "be in good spirits."
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 Marius Hancu's reply was promoted to an answer.
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