HSS ultra light for all season except I use a "seat of the pants original" which has un-trimmed straps for late winter because it can easily go over all the heavy layers I'm wearing (I will also use the SOTP when I'm in a tree with a Ghillie on) ,,,, when its that cold the HSS vest pockets are useless I need warm wool jacket pockets with nothing blocking them.
now the HSS can be worn under everything but I have that lanyard strap coming up out of the back of my collar which causes a 10 degree draft down the back,,,, my setup if fully tested by me so I'll vote a 10 every time.