If you know what will be in the view, you can also set the default value from Controller as well rather then set up it into the view/cshtml file. No need to set default value from HTML side.
In the Controller file.
commission.TypeofCommission = 1;
return View(commission);
In the .cshtml file.
@Html.DropDownListFor(row => row.TypeofCommission, new SelectList(Model.commissionTypeModelList, "type", "typeName"), "--Select--")