Retaining Records Of Top N Rows And Deleting The Rest

Hi All,
I am writing a SP where I need to pass an value to maintain records of last n days. In this SP I am deleting a couple of tables based on the value passed to this SP. For e.g. If the SP is passed the value 10, then only TOP 10 records is maintained, the rest are deleted.
I have formed the following logic, which I feel can be improved vastly.
I create a temp table and

CREATE TABLE #TempAuditTbl (Rownum int PRIMARY KEY, Orderid uniqueidentifier)

INSERT INTO #TempAuditTbl

SELECT ROW_NUMBER() OVER (ORDER BY orderdate desc) AS rownum, Orderid FROM Orders

DELETE Orders FROM Orders INNER JOIN #TempAuditTbl adt ON adt.Orderid = Orders.Orderid AND rownum > @TopnRows

DROP TABLE #TempAuditTbl


OR


DELETE FROM Orders WHERE orderid NOT IN ( SELECT TOP @TopnRows OrderID FROM Orders ORDER BY OrderDate desc)

This way I am able to keep the top n records.
Which of these two solutions is more efficient? Is there a more efficient way to achieve the same.
Please help.

Thanks & regards
Sunil