What should be the quality of Japa?
By and large, japa is a personal matter. Whether a person is chanting their rounds or not is ultimately very subjective, and should not become a matter for public discussion. For instance, someone might say that they've chanted 16 rounds, but who is to know what the quality of those rounds was, or how many offenses may have been committed while chanting? Although Srila Prabhupada recommended that we chant 16 rounds each day, he also made clear that quality is ultimately more important than quantity. If one finds that they have to chant poor rounds in order to get their 16 rounds done, it's better for them to chant fewer rounds and do them nicely.
"These are different, nine processes. Sravanam kirtanam. Sravanam means hearing, and kirtanam means chanting, chanting. So by this process… Just like I chant and you hear, and you chant and I hear. Parasparam. Bodhayantah parasparam. This is the factual activities of devotion in devotional society. This bodhayantah parasparam: I chant, you hear, and you chant, I hear. So by this process, the transcendental name, the sound incarnation of the Supreme Lord, becomes manifest, manifest so that we can realize God simply by chanting and hearing. Simply by chanting and hearing that will be realized. Of course, there are some rules and regulations for chanting, but in the beginning we haven't got to observe those rules and regulation at the present. First of all let us have the taste for chanting; then we shall be little careful that the rules and regulations are followed."
– Srila Prabhupada Lecture, 09-08-66, New York.