Cablelocks are neon signs that advertise to crooks: "Free bike Right Here". The cable locks that are as tough as a five pound u-lock weigh eight or ten pounds. So, the five pound u-lock is the best combination of weight and security.
If you live in the sort of city that has skilled crooks targeting bikes, you need to avoid riding an obviously expensive bike (a really nice 1988 bike with Shimano 105 rides well, but does not interest a "pro" who steals bikes).
And, if your bike will be out of your sight for more than two minutes, you need high quality u-locks. the two pound models from Kryptonite and OnGuard work well in safe neighborhoods for a thirty minute shopping trip. But, if your bike will be parked for eight hours at a time, or after dark, you need the BEST, which would be the Kryptonite Fahgettaboudit u-lock, or the Kryptonite New York u-lock.
When I go to baseball games at night in downtown Houston, I have a Kryptonite New York lock around the rear wheel and a steel post set in concrete, and then a two pound u-lock, such as the OnGuard Pitbull, around the front wheel and a locking post, or at least attaching the front wheel to the frame.
And, if I'm going downtown, it is on a 20 year old bike...which I park next to the newest Cannondale or Trek I see...crooks prefer new and shiny bikes that are easily pawned over rusty, scratched vintage bikes, no matter how good that old bike actually is.