Response Content type as CSV
Using text/csv is the most appropriate type.
You should also consider adding a Content-Disposition header to the response. Often a text/csv will be loaded by a Internet Explorer directly into a hosted instance of Excel. This may or may not be a desirable result.
Response.AddHeader("Content-Disposition", "attachment;filename=myfilename.csv");The above will cause a file "Save as" dialog to appear which may be what you intend.