IMO, the most effective is the hardened hex chain with a heavy lock. No, nothing's theft-PROOF, but some things are a better deterrent than others.

I did a little test last year at work; a 3/8" thick cable lasted 10 seconds with an 18" bolt cutter, and about 20 seconds with TIN SNIPS.

That doesn't mean they're useless, though; in combination with another type of lock, cables can be bewildering, which is why I still use the 9' long 3/8" cable with a U-lock. One hoodrat kept talking about my "Pee Wee Herman lock", when I had the cable twined around four bikes, along with a chain around all four downtubes. But the bikes were still there.......

We've had three events; two happened to the same nephew. The first, when he was 10, some hoodrat punk a couple years older just walked up, got on it, and rode off. The second, when he was 17, he borrowed my sister's bike, locked it only through the frame, and came out of the store to see no wheels. (Come to think of it, the last I saw her bike, he had it again (he's 23 now), and is "between homes". Dunno WHERE the bike is.

Some other neighborhood punk tried to take off with my daughter's bike when she was 10; no sooner had he straddled it than she took off after him. He dropped it and fled.

NOTE: a bike mechanic friend once told me NO lock was safe, because they could all be "frozen" and shattered by a CO2 fire extinguisher. 90% of what he told me over the years, I quietly said "Whatever" to.........