What are the key differences between sole proprietorships, partner- ships, and corporations?

What are the key differences between sole proprietorships, partner-
ships, and corporations?
How do some firms get to enjoy the benefits of the corporate form
of organization yet avoid corporate income taxes? Why don’t all
firms—for example, IBM or GE—do this?
Why is the value of a business other than a small one generally maximized if it is organized as a corporation?