My bike weighs enough (112 lbs.)so that most of the time I can just free lock it (U-lock through front wheel and frame). I also live in a fairly low crime area.
I have and carry three different locks. What gets used depends on my assessment of the area:
Low risk-- I generally free-lock the bike
Higher risk-- I use the cable and padlock around the frame and rear wheel & something solid as well as the U-lock through the front wheel and frame.
Higher risk-- I use the above methods and a square linked, hardened steel chain through both wheels,frame and something solid.
If I feel the area is sketchy enough I won't leave my bike alone there.