Breathing exercises affect people differently, so it's hard to give a general answer. However, let me explain the two exercises you mentioned: kapalbhati and bhastrika.
Kapalbhati is both a purifying exercise and a breathing exercise. To do it, you exhale forcefully and contract your abdominal muscles, which massages your organs and clears your respiratory passage. Many people like this exercise.
Bhastrika is different. You inhale and exhale forcefully in this exercise, which you usually do while sitting. It can help you have better lung capacity and less stress.
Breathing exercises affect everyone differently, so there is no one-size-fits-all answer. Kapalbhati is a breathing exercise that involves forceful exhalation and abdominal muscle contraction, which can help clear your respiratory passage and massage your organs. Bhastrika is different, involving forceful inhalation and exhalation to improve lung capacity and reduce stress. Both have benefits, but kapalbhati is my personal favorite because it focuses on abdominal breathing and respiratory clearance.