I do neither one nor the other. I start with an intro package of 3 sessions plus the screening. After that, I bill my clients on a monthly basis. I never get into the selling of packages or commitments of any sort.
I have operated like this for the last 18 years, and it has worked very well for me.
The only exception to this approach is the training in MELT which I have started as a separate entity a few years ago. Here I do individual sessions or courses of defined length. Since the concept of MELT is to teach people to self-treat, is has worked for this unique scenario.