I have a newfound respect for U-locks........
Bought a Columbia Metro (minor classic) at the local Goodwill a couple of months ago, all of $ 15.00, Kryptonite U-lock around the frame.
They did not have the keys, so I dropped it off at a locksmith to have keys made.
Got a call from the locksmith that the lock was smaller than standard, and all he could do was remove the lock, but could not make keys.
Too bad, I would have liked to be able to use the lock, looked almost unused, but I decided to 'just' hacksaw the lock off myself.
Well......
Neither hacksaw nor files could make even a dent, I ended up buying a 36" (!!!) bolt cutter, took about an hour or so of chewing, chewing, chewing away with that thing - leaning all my weight into every chew - before I FINALLY had enough of a 'cut' for the hacksaw to bite.
Another hour or so of hacksawing.......
I'm sure the kids down in the warzone would have had that lock cracked in 3 seconds flat.......
However....there is a bike frame U-locked to the bus stop sign just a little ways from my place, has been there for at least 8 months.
Just the frame, everything else has been vandalized off the bike (looks like some sort of off-brand MTB), I guess no one has wanted to tackle the U-lock.....
The best lock is still to not leave your bike outside, in this town, they'll steal or vandalize anything, even a Huffy......