Note no. 1
THD of amplifier is most imp
It was related to distortion of signal output it should also destroying RMS POWER it should be seen how much should less that much better sound quality
It should 1%

Note no. 2
Signal to noise ratio
It basically relates to all unit equipment that all have some noise by there electron if the had noise of electron 10 dB then our amplifier should give more the 10 dB
Should be seen how much more it was sound quality was that much good
It should more than 103 db
Minimum 92
Max how much we can afford

Note no. 3
Slew rate
How much fast your amplifier act to take signal or given signal
Minimum 20 mid quality
If 20 mean hf frequency was too good
Jitna Jada hoga utna hf frequency was good