Which Bike Lock is the Best?

Scott Elder wrote a very useful review of the best locks for your bicycles:

... I always feel a twinge of fear when I leave my bike on the street, worried that upon my return, I'll find nothing more than a busted U-lock.

... —in the fall of 2004, bicyclists discovered that many round-key U-locks could be picked with the plastic barrel of a Bic pen. Kryptonite, which caught the most flak from the scandal, exchanged more than 380,000 locks for pen-proof, flat-key models free of charge, and lock competitor OnGuard, which had already phased out round keys, got a big sales boost. Today, flat keys are the norm.

... To find out which locks work best, I pitted nine locks against each other from Kryptonite, OnGuard, and Master Lock: five U-locks, two woven steel cable locks, and two heavy-duty chain locks.