An S corp has a number of limitations on how many stocks can be made available as well as just who the shareholders can be. However, the LLC does not have such legal limitations.
If you actually create an S corp, your company can only have 100 shareholders. Additionally, only one class of stock is permitted. The LLC does not have these limitations, creating another advantage for those grappling with the issue of whether or not to actually pursue a full S corp structure.
Another potential advantage an LLC structure has over an S corp is regarding U.S. citizenship. All shareholders must be legal U.S. residents or citizens. While this may seem easy to control, keep this in mind. If one of your shareholders dies and leaves his share to a child or spouse who is not a U.S. citizen, your corporation could automatically lose its corporate status.
Additionally, an LLC is not barred from having other corporations as shareholders. However, an S corp is. The corporation must have only individuals or approved trusts as shareholders.