Most secure Password regular expession validator

<asp:TextBox ID="txtPassword" runat="server" style="margin-bottom: 0px"></asp:TextBox>
<asp:RegularExpressionValidator ID="RegEv" runat="server"
            ErrorMessage="RegularExpressionValidator"  ControlToValidate="txtPassword"
            ValidationExpression="^(^.*(?=.{4,8})(?=.*\d)(?=.*[A-Za-z])(?=.*[@#$%^&+=]).*$)$|^(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).{4,8}$|
            (?=^.{4,8}$)(\w*(?=\w*\d)(?=\w*[a-z])(?=\w*[A-Z])\w*)$
            |^(^.*(?=.{4,8})(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=]).*$)$"></asp:RegularExpressionValidator>