There isn't a definitive answer that's true for every mISV.
The best resource I've read to help you think through the options is LLC or Corporation? How to Choose the Right Form for Your Business from Nolo press. It's written by an attorney for small business owners. It contains a good overview of the issues and considerations.
S-Corp is ideal for a company with fewer than 30 employees and a non complicated ownership/ profit sharing structure. A S-Corp avoids the double taxation associated with corporations by passing profits directly though to the owners at their percent ownership. They also provide legal benefits by sheltering the owner’s assets from litigation in some cases. An S-Corp cannot be formed with more than 30 employees.
Which jurisdiction(s) will you be operating in?