Does one mode make a difference over another?

Yes, I agree that person or in face is always best!  I usually like to have an face-to-face conversation and will follow-up with an email if the situation warrants it.  I caution to junior officers that you do not always want to deliver “bad news.” Remember, leaders are human beings too and they shouldn’t be conditioned to hear bad news every time they see or hear from you.

Does it make a difference when the leader is a staff officer versus a commander? An officer versus an NCO?

No.

Got a good “effective communication” story to share? Perhaps an “ineffective communication” story?

I would be careful to not always  deliver “bad news.” Remember, leaders are human beings too and they shouldn’t be conditioned to hear bad news every time they see or hear from you. On a similar note, proofread your texts or emails prior to sending!