Tighter fitting U-locks are considered safer, because it gives thieves less space to manuever a cutting tool. Even the bigger shackle locks have recommended locking techniques to get the lock as tight as possible to the frame.

I have a NY Faghaboutit, full size. It's my secondary lock when I know I'm going to be leaving my bike someplace that could attract attention. It's far too heavy to be a practical everyday lock, I have a lighter lock I use for everyday use.