I am exploring the possibilities of ASP.NET MVC in the example webapplication of Visual Studio the WebMatrix.WebData.WebSecurity is used for Membership (creating accounts, a
The main differences between old ASP.NET Membership provider and SimpleMembershipProvider are explained in this good article - http://weblogs.asp.net/jgalloway/archive/2012/08/29/simplemembership-membership-providers-universal-providers-and-the-new-asp-net-4-5-web-forms-and-asp-net-mvc-4-templates.aspx
It is better to use SimpleMembershipProvider (WebMatrix.WebData.WebSecurity) than old ASP.NET Membership Provider (or Universal Providers)