What is usually the easiest form of business to start and end?

This is easy for you to work out purely from common sense. So permission, agreement, contracts and so on must be sorted out before a business can either start or end.

In a sole proprietorship, a person can effectively just say 'I've had enough' and walk out, or 'I'm going to sell my graphic designs online' and get going. He has only himself to please, harm, benefit and/or blame for the success, continuation or end of his business. A hand knitter producing baby jackets for the local shop is a sole proprietor.