You can choose two fabric types for your aerial performance - low stretch or stretch. For aerialist who just a beginners and have to practice with ceilings less than 13ft (about 4 meters), it's always better to work with low stretch fabric. You do not need medium stretch fabric if you just learning the aerial silks and you do not have high rig points.
With higher rigging points, higher ceilings you will begin working with longer drops and falls, roll ups, flyings, probably it's the time when you may prefer the medium stretch fabric, because it will give you a nice smooth bounce during performance.
It is absolutely personal preference. When you have ceilings higher than 13ft and begin working with longer drops and falls, you may prefer the medium stretch fabric because it gives a nice bounce when performing.
Absolutely, it's a personal preference and only you can decide which one is better for you. Most popular is a low stretch fabric. For example, aerial couples mostly using low stretch fabric and never use medium stretch, to make sure they will have a more accurate take off feeling.