Should I form my company as C corporation, an S corporation, an LLC, a partnership, or a sole proprietorship?

Start it as an S corporation, unless you have to issue both common stock and preferred stock; in that case start it as a C corporation. And an S corporation can easily be converted later into a C corporation. LLCs are popular but can get overly complicated. Partnerships and sole proprietorships are to be avoided because of the potential personal liability to the owners of the business.