For me, there is no BEST way. Four factors to consider are:
1) Your relationship with the person.
2) The subject matter & how important or delicate it is and
3) How easy or difficult is it to reach that person.
4) By which mode are you a better communicator?
I have a schedule that is unusual for most people, so it is nearly impossible to reach me in the evenings by phone, yet I am usually awake and starting the day while most people in my time zone are sound asleep, so it is easier to get in touch with me via email or text. I respond promptly to most emails.
Some people are more comfortable and thus express themselves better by writing, others do it better by phone or in person.