Neither. Smart wool socks from LL Bean or Cabelas inside Sidi Canyons keep my feet warm enough in cold weather. My Gerbings heated jacket liner is another story... I don't ever ride in cool weather without it. Keeping your core warm goes a long way in keeping your distal extremities warm.
For the feet, it depends on how cold it is and how long you're going to be out. Merino wool socks and good boots work well for me at 20 degrees F for two hours, but I start to really feel it an an hour and forty five minutes. That's why I bought heated insoles -- much more comfortable for a three hour ride.
Salty Fog Rally 2007, 2009, 2011, 2012, 2014 AND LOOKING FORWARD TO 2015!