Depends on what a person is going through.
When a person is feeling particularly frail, mussar might not be the best approach.
Though I’m generally more a mussar person, I’ve a big need for chizuk right now, so I’m swinging that way.
There’s a time and purpose for everything.
Chizuk, we should always emphasize the positive, The Haflaah in Panim Yafos says uvocharto bachaim, chose life. Remembering the day of death should be the last resort,
Im a little biased on this issue because of my upbringing, but in my community mussar is extremely frowned upon. You gotta be positive not negative. some times you gotta give mussar but even then it should be in a soft way while injecting chizuk into there.
The holy Shlah explains the pasuk in Mishli אל תוכיח לץ פן ישנאך. when admonishing someone don’t call him a fool as he will hate you, הוכיח חכם ויאהבך, call him a chacham, the wise one and he will love you. Also the Rav Abarbanel says, לא תשא עליו חטא, don’t put the sin on him by labeling him. Maybe rather say that people do instead of you do.
The Sefer Habris writes that דרך חיים תוכחת מוסר can be taken to mean that Mussar should be given by way of Derech Chaim. In other words, the right kind of Chizuk is the best Mussar. Rabbi Chaim Palagi quotes this piece and praised it.