I own those three U locks that are supposed to be pretty secure, and was wondering how easy their locks are to pick by professionals:

I don't know about the other two, but the Knog Strongman has a "High security disc style lock barrel with over 5000 unique key variations".
One day while we were at the movies, a friend got her (expensive) Brompton bike stolen that was locked on the street with a Kryptonite Fahgettaboudit to a solid fence. Since employees standing a few feet from there heard nothing, an angle grinder seems unlikely, so I suspect the lock was picked. Hence my wondering about how secure bike U locks really are.
Thank you.