Which is better L293D or L298N?

Can anyone tell me what is the difference between motor driver L293D and L298N and also about H-bridge and F-Bridge. And also does do we need any external power supply to run the motor in L298N. I am little bit confused. Can any one explain it to me. That will be helpful.

In L293 all four input- output lines are independent, while in L298 , a half H driver cannot be used independently, full H driver has to be used. Protective Diodes against back EMF are provided internally in L293D but must be provided externally in L298 / L293 .

Can you mention Why diode is used in L298N and also what is back EMF.

Back EMF is the system in the coil of an electric motor that opposes the current flowing through the coil, when the armature rotates. … At high speeds the traction motor armatures are rotating rapidly and have a high back EMF

They suppress the inductive transients from the motor to protect the L298 transistors. If you look at their polarity, you will seed that all the diodes are reverse biased expect for transients below ground or above the power supply voltage, so have no effect on the normal drive voltages.