Delaware is NOT the cheapest, but it is extremely flexible (both legally speaking and administratively speaking - there are very few states where you can pay a premium and find someone to come in on a holiday/weekend to file your restated charter to close a big deal), and it has a very well-established body of law. That means everyone knows what to expect. Think of it like a really great WYSIWYG editor, whereas other states' laws can be like coding a site in a brand new alpha release programming language.