How polar encoding works?

How polar encoding works, and which one of all encoding type is better? 

Polar encoding uses two voltage levels: - One positive and one negative. When the digital encoding is symmetrical around 0 Volts, it is called a Polar Code. The RS-232D interface uses Polar line encoding. The signal does not return to zero, it is either a +ve voltage or a -ve voltage.
Bipolar encoding is better than unipolar encoding.