Even on my 'bents, my first choice is regular bike shorts with a pad. The pad is the underwear and it provides chafing protection and sweat control. My second choice is unpadded lycra shorts with lycra boxer-style underwear. Again, for protection against chafing. Cotton retains moisture and chafes the worst of any fabric choice. Plus 'whitey tighteys' have a rolled hem right in the corners where it can do the most damage.