Most bike thieves don't pick locks I think.
That said, I do not know how well these flexible cables and chains compare to solid U-Locks when it comes to resistance against cutting. I still prefer U-Locks. It is a bit harder to find a suitable piece of street inventory to lock the bike to, but when the bike is locked to something suitable properly it might become hard for the thief to get a good attack point to the U-bar with his tools because ideally everything is tight and the lock can't be moved. His tool might therefore be useless or risk damaging the bike.
I have the problem that there are usually not a lot of more expensive bikes on the road to park next to, so I usually put the bike in a well-lit and well-visited area (lots of watchers, pedestrians, etc.) and use two U-locks to secure rear wheel+frame+sign post and front wheel+frame with the shorter lock. Apart from that, I never park it overnight, never for too long. If you are visiting friends, ask them if they'd mind you putting the bike in their basement, on the balcony or in the garage for the duration of your stay.
Again, if I had to use a flex lock, I'd look for a chain, like in this Abus product:
http://www.abus.de/de/main.asp?ScreenLa ... 3318125287
Again, I am not sure if chains are more resistant to steel cables, but I think they might be for some reason. Apart from that, I have seen electronic devices on sale that mount into your seatpost and emit a very loud when the bike is moved a little bit while the alarm is activated. This may or may not deter thieves, depending on the situation and the location the bike is parked. I think bike thieves are easier to scare by this than car thieves, because they don't expect it, and they will most likely have to move the bike a little prior to cutting the lock to get the cutters in. If the alarm sounds in this situation they might just as well run and pass on the bike. Or they might be properly pissed and come back later with an advantage...

Due to financial limitations the light at the end of tunnel has been turned off until further notice.