Premanand Maharaj Ji

Which is better, doing good deeds or doing bhajan, and how do I know what is truly good?

Bhajan clears the mind to see what is good

Good deeds and bhajan (devotional worship) are not two things. Bhajan purifies the intellect, and only a purified intellect can know what is good.

Without a purified intellect you cannot know what a good deed is. And the intellect is purified by bhajan.