The top end Kryptonite locks such as the NY series along with the top end Abus U locks are supposed to be the hardest to break. The NY Forgetaboutit (?) locks also have large enough shackles (18mm) so that most chain cutters jaws will not open wide enough to even fit them. Per what I read a British magazine test took 10 minutes to get through a NY Forgetaboutit with an angle grinder while the steel in the same diameter shackle lock from OnGuard was cut in about 2 minutes.
No such thing as an indestructable lock unfortunately.
__________________
Gear Hubs Owned: Rohloff disc brake, SRAM iM9 disc brake, SRAM P5 freewheel, Sachs Torpedo 3 speed freewheel, NuVinci CVT, Shimano Alfine SG S-501, Sturmey Archer S5-2 Alloy. Other: 83 Colnago Super Record, Univega Via De Oro
Visit and join the Yahoo Geared Hub Bikes group for support and links.
http://groups.yahoo.com/group/Geared_hub_bikes/