Originally Posted by
KimLaroux 
Best Anti-theft is to never leave your bike locked anywhere. Any lock will be broken by a motivated thief. And cables are useless. You can cut even half inch cables using a handheld wire cutter. It looks like you're just unlocking the bike. A thermally-treated chain of the same size will need a 4 feet long bolt cutter, with one handle on the ground and all your weight on the other. It's a bit more obvious to a passer-by what's going on.
A good advice is to use two good locks of different technologies. Most thieves carry tools to break a single type of lock. Thieves are lazy too, so they'll take the bike easier to steal. And for those who think that using a cable locked trough a U-lock is using 2 locks, it's not. It's no safer than using only the u-lock - once the thief breaks the u-lock, the cable is gone. If you're gonna carry a cable and a U-lock, use a cable with it's own lock. This will give you two independent locking systems of different types, which will need two different tools to break. A LOT safer.
The cable is secured trough the same U-lock that locks the frame. A thief only has to break the u-lock, and the bike is free. If you carry a cable with it's own lock, then you can secure the front wheel and the frame to the other pole of the stand. This way a thief has to break the u-lock using one type of tool, and the cable using another. Unless of course he's carrying a disc grinder, at which point no lock in the world will stop him.
Personally, I use a chain. I used a cable but my bike was stolen within the month I bought it. With luck, the police found it the next day. The thief was nice enough to leave me my cable.
The chain is just long enough to wrap both wheels and the frame. It's the strongest chain my local hardware store stocks, but it's small compared to other bike chains. I don't think I'd want to carry a larger one for commuting. It gets way too heavy and cumbersome. When I move to a larger city for University, I'll simply stop using my bike to commute. It's just not worth it.