+1 on "auto". I set it and forget it. I'm not sure why the AC button is on when it is 23 degrees outside (Fahrenheit, my metric friends) but it does keep the car comfortable throughout.
Just curious as to whether the AC is truly on (and sucking gas) or if it is in some sort of standby mode... no worries; I'll post the anticipated response myself...
and go do a little research!