For scratches? The Whitestone Dome, if you don't mind the price. Otherwise, they'll all fail to stick in the middle, fail to stick at the edges, produce moiré patterns or other problems.
For break resistance? You'll have to wait until Mr. Scott invents transparent aluminum. Screen protectors don't work as well as TPU cases with a lip that extends past the screen. (And if you drop a phone with a glass "screen protector" screen-down right where there's a pebble with a sharp point, the screen protector and the screen will both break, unless a case is keeping the protector from hitting the pebble.)