Your question has been answered dozens of times in various threads about locks and security. One thread in particular is a "School for Crooks". I'm not mentioning anything that has not been posted many times before, so....

The "Your Brand New New Bicycle U-lock In Not Safe" thread at the top of "General Cycling" has over a thousand posts. During the first hundred posts, several guys teach you everything a crook would need to know to steal a bike. But, for each guy who posts to brag how quickly he can open a lock with a BIC pen, five guys post to say they failed. A thousand posts in that thread, and only about twenty guys who claim any great "prowess" at the pen trick...and their success is at the kitchen table with THEIR own lock, not on their knees, next to a bike rack, working on someone else's lock.

The BIC pen thing was a bit of a hoax...a pen is about the HARDEST way for the majority of people to open a randomly selected U-lock that is correctly attached to a bike and to a bike rack. (The guys who brag about using a BIC pen have never claimed any great success meeting each of THOSE conditions).

Every lock comes with a spare key. That is the fast way to open the lock. Leverage attacks can do more damage to the frame than to the lock (if it a Krytonite, and not a Wal-Mart brand lock...those fall apart with a good yank on a leverage tool).

So, cutting is the best way to go if you don't want to risk damage to the bike. Two minutes with the correct power tools. A couple hours with a hacksaw and several new blades.