You can use any of the methods to add a parameter along with its value, but Add is deprecated because it has a similar overloaded method. So when using Add, you will have to be careful to make sure that the compiler understands that it is a value and not a SQLDBType. So its always better to use AddWithValue method. Check out this link from MSDN for reference.
http://msdn.microsoft.com/en-us/libr...withvalue.aspx