Yes, self insurance is always better if possible, since that means your cost is exactly equal to your risk. When you buy third party insurance, your cost is going to equal your risk + profit + overhead for the insurance company.

You self insure when you can afford the max cost you could incur (e.g. You could buy a new car if you had to.) You buy insurance when you can't afford the rare but very costly catastrophic loss - life insurance, health insurance, car injury insurance.