Aussie bike-accessory maker Knog's easy-to-carry rectangular U earns our acclaim. Although tricky to lock to frame, rim, and railing, the 13mm steel shackle withstood our bolt cutters and barely showed a mark after 10 minutes of furious hacksawing. Our grinder cut through in 1 minute, 45 seconds, but not before bucking enough on the lock's silicone coating to send most thieves scrambling. [$100;]