Eggplant Jeff

A oxy/acet torch is definitely a "quick" way to break any lock. Whether it's the fastest will depend on how susceptible the lock is to other methods. A cable for example, will burn through in seconds... but a single snip from a pair of cable cutters is faster.

Any kind of hardened steel will be roughly the same time depending on thickness. Some of the "non-torch-cuttable" metals (like stainless steel) don't cut, but for purposes of breaking a lock it doesn't matter. They don't "cut" because the metal doesn't burn through; however it still reaches its melting point and the gas from the torch will "push" the molten metal away. The "cut" is ugly as hell, sloppy and molten metal dripped around and stuff, but if your only goal is to turn one piece of lock into two pieces it'll do it.

Plus a torch easily combines with any other method... Take the toughest hardened steel lock, heat it for 10 seconds with a torch, let it cool off, the steel now has all the temper out of it and will cut easily with a normal method (hacksaw or whatever). Or heat it and apply your lever, it'll bend like soft plastic.