DbType.String vs. DbType.AnsiString

Although both DbType.String and DbType.AnsiString deal with character data, these datatypes are processed differently, and using the wrong data type can have a negative effect on the application's performance.

DbType.String identifies the parameter as a 2-byte Unicode value and is sent to the server as such. DbType.AnsiString causes the parameter to be sent as a multibyte character string. To avoid excessive string conversions, use:

DbType.AnsiString for char or varchar columns and parameters.
DbType.String for unichar and univarchar columns and parameters.