There are so many types of locks: chain locks, cable locks, U-locks. For this reason you should consider what your lock should fulfill before you buy it.

People who drive much and park their bikes at the station need a lock with a higher security level than people who sometimes park their bikes at the beer garden.

Generally you can say that lighter locks like spiral cable locks offer minor theft protection. In contrast high quality U-locks and chain locks are guarantors for the highest safety - with correspondingly higher weight.