Thanks for your question! It’s better to get your own insurance for a few reasons. When you’re listed on your parents’ policy, most often you’re listed as a driver and not a named insured. Most finance companies require you to be the first person on the policy or a named insured when you buy a car through them. If the car is registered in your name, it should also be insured under your name.
Most often, at the age of 21, insurance companies are going to want you to have your own policy either way.