Tests by "Bicycling" and "Cycling Plus" have shown that Master locks, at any price range, are junk. They can be opened in a couple of seconds. Why do people buy locks that fail test after test? A real mystery.
The May 2007 "Cycling Plus" has their latest test results, which are consistent with the test results at "Soldsecure.com". Those tests consistently show that the best u-locks from Kryptonite match up well against the best locks from Europe's best lock supplier, Abus.
The "best" u-locks that are easy to find in the USA are the Kryptonite New York u-lock and the Kryptonite Fahgettaboudit u-locks.
Such heavy duty (and just plain heavy) u-locks may be more than folks need who live in "Friendly Village" and who are locking up a $300 or $400 bike. For low-risk situations, the light weight mini u-locks, such as the OnGuard Bulldog, the OnGuard Mini TC, and the Kryptonite 2000 mini u-lock are a good balance of light weight, portability, and a reasonable level of security.
To see soldsecure's test results, go to:
www.soldsecure.com/Leisure.htm
And, consider going to Barnes & Nobles or Borders Books and picking up a copy of the May issue of "Cycling Plus" with their latest lock test results. Every issue is well worth the USA price of $8 a copy...a terrific cycling magazine.