You could do something like:
DECLARE @operation as Varchar(10);
DECLARE @Count as int;
SET @operation = 'Inserted';
SELECT @Count = COUNT(*) FROM DELETED;
if @Count > 0
BEGIN
SET @operation = 'Deleted';
SELECT @Count = COUNT(*) FROM INSERTED;
IF @Count > 0
SET @operation = 'Updated'
END
HTH,
Rob