What are the best increases to use. I only knit hats
Best is pretty subjective. Depends a bit on where you put them and the type of fabric you’re making. Ysolda Teague has a great post showing several options for comparison.
lewister is correct. Depends on where they are done and the pattern. Do you have a pattern for your hat?
Best is such an open question. I try to use increases that a practically invisible. Some increases stick out like a sore thumb and others just blend right in and are practically invisible. It does depend on the pattern and sometimes if there is an increase you favor over another. You are the creator and it is your choice.