How to Choose a Lock for NYC Streets
When figuring out your locking situation, it's important to consider the three general levels of
Level 1: The Hooligan
The hooligan is dishonest but he is not a professional criminal. He certainly didn't leave the house with any tools on him, and maybe wasn't even thinking about stealing anything until he saw your bike. He might remove your lights or other components that aren't bolted on (e.g. quick release seat and wheels), or see that you've missed the pole completely and ride away with your bike.
Lock your frame to a secure pole. If you have quick release components; lock them, replace the quick release with a bolt, or take the parts (lights, seat, etc) inside with you.
Level 2: The Amateur
The amateur has left his house (usually at night) with bolt cutter or a hand saw, maybe a hammer and chisel, and a clear intention to steal a bike. He has a general idea of what bikes and parts are worth, and how long it takes to get through certain locks with the tools he has.
Level 3: The Professional
The professional has left his house (almost always at night) with a battery powered angle grinder and cares very little about how good your lock is, he knows he can get through anything and is looking for the most valuable bike he can find. He may even bring a van, cut the pole and worry about the lock(s) later.
Don't have the nicest bike on your block.