Stopping a DC motor using an H-bridge: forward+backward vs. 'brake'
It all depends on what you want to do.  Both methods are perfectly valid for different situations.

The switched-short method doesn't "stop" the motor.  It merely turns the motor into a generator and applies a very large (short circuit) load.  This makes the motor harder to turn, slowing down the motion until it finally stops.

The rapid forward-backward clamps the motor in a position causing a very rapid stop. It also uses an awful lot of power to do it, and generates massive amounts of noise.

So it all depends on the effect you are after.  A gentle deceleration to a stand-still, which is most often desirable for things like slowing an electric vehicle, or an abrupt stop, which is good for robotics where you need to get to a specific position and stop right there.  It's a trade-off between precision and efficiency.

In a side note, the switched-short method can be expanded out to create what is termed "Regenerative Braking" where instead of shorting the motor out it is used to recharge the batteries that run the motor.  This is widely used in electric vehicles to reclaim some of the energy wasted during braking.