All any lock will do is deter an opportunist or delay a truly dedicated thief.

The only bikes I've ever had stolen were just not locked up. On the flip side, I once had the opportunity to cut my snazzy Specialized cable lock with my hacksaw. I was able to get through this big, fat cable in 45 seconds. Nobody tried to stop me or interrupt me. Very rare situation when you get to "steal" your own bike.