Originally Posted by Winfried

Probably, but a friend got her expensive bike stolen while locked with a heavy-duty U lock (Fahgettaboudit from Kryptonite) to a lamppost on a busy street just a few meters from the cashier of a theater; They heard nothing, we found no trace of theft on the premises although I doubt the thief would sweep afterwards. Thus, it's likely that this was done by someone who does know how to pick locks. With the right tool and the right experience, it only takes 1-5mn to pick a lock:
https://www.youtube.com/watch?v=LYv4uq_eML8

Numerous bikes have also been stolen while "secured" with Abus Bordo locks:
https://www.youtube.com/watch?v=GMc6vwWiQIk

The question I had is: Do U locks use different types of locks? If that's the case, is it possible to tell the type used by looking at the key, and which one is the most secure?

Thank you.