Choosing a business legal structure influences the day-to-day operations of your business. It affects how much you pay in taxes, your ability to raise money, the paperwork you need to file, and your personal liability. You also need to choose a structure before register your business with the state, get a tax ID number, or file for any licenses and permits.
Choose carefully. While you may be able to convert to a different business structure in the future, there may be restrictions based on your location. This could also result in tax consequences and unintended dissolution, among other complications.
Consulting with business counselors, attorneys, and accountants is always the best option.
Below is a chart from the U.S. Small Business Administration, along with more detailed information.