What is a more secure bike lock? Steel chain link? or steel cable?

I'm thinking steel chain if it's thick enough. How thick would it need to be?

Other answer:

Alex:
You get what you're willing to pay for. A good set of keyed U and cable locks will cost around $70.
Tim D:
The one you can carry and use every time, huge chains or cables are all very well but if you cannot transport it and use it then it is useless. And any lock or chain can be defeated given enough time.
LandRiderJerry:
You get what you're willing to pay for. A good set of keyed U and cable locks will cost around $70.
adam:
most of my bikes are OLD and have drum brakes in the rear with no front brake at all. Disk locks are no good for them. Carrying a heavy chain? Where would I put it? I carry a U lock. Kryptonight. At home they are all chained up and my gate is locked and I have several Pit bulls in my yard.
Keith:
15 millimeter Steel cable, the cable is generally are to big to get a bolt cutter around it.
Parker:
the one you can carry and use every time, huge chains or cables are all very well but if you cannot transport it and use it then it is useless… and any lock or chain can be defeated given enough time…
Lupita:
you get what you're shalling to pay for… a good set of keyed u and cable locks shall cost around $70…
vulcvoy:
Locks only keep honest honest. If a thief wants your bike, they will take it. You just want to be harder to take the the other guy.
Good luck and ride safe.
Ernesto:
locks only keep honest honest… if a thief wants your bike, they shall take it… you just want to be harder to take the the other guy…
good luck and ride safe…