I have recently started using Request(\"key\") instead of Request.QueryString(\"key\") to access my querystring values. However I have read that:
Request(\"key\")
Request.QueryString(\"key\")
They're checked in the following order:
QueryString
Form
Cookies
ServerVariables
The search is short-circuited, so as soon as a matching key is found the value is returned.
So, to answer your question, a matching QueryString item takes precedence over Cookies.