Well the clutter on the site is shocking, its the worst of the commercial web,
And this particular circuit is a bad circuit, avoid.
With low voltage H-bridges you have several options:
NPN + PNP bipolar
n-channel and p-channel MOSFET
An H-bridge chip (preferably not darlington based).
relay H-bridge (no PWM possible, only forward/reverse)
For higher voltages the options include darlington drivers
since the 2.5V overhead is less wasteful at 24V or 48V.
Its less sensible to use NPN/PNP and n-channel/p-channel
bridges at higher voltages as the driving is complex (more complex
than the bridge!).
n-channel only MOSFET H-bridges with high/low MOSFET driver chips
come into their own for high current / high power bridges upto 100V or so.
The MOSFET drivers bootstrap the gate driver supply automatically. Such
bridges have the nice property that the motor supply and driver supply are
independent, either can be powered up or down without having to worry
about back-powering or anything like that.
higher voltages and IGBTs start to take over as they handle high voltage
transients more robustly than MOSFETs