Stupid Power Conditioner question but...

If you are going to run any nice gear without surge protection (and you should rarely do this) then at least install a whole house surge suppressor.

There's really no practical difference in a 15A vs. 20A circuit except for the minimum gauge of wiring required.  12 ga. vs. 14 ga. which with a long run can give you a bit better voltage performance.

@OP
+1. The whole house surge protector is the best way to safeguard against power surges, not only for your stereo equipment, but your computers, as well.
@erik_squires @jea48 ,
Always great advice.
Bob

“I would plug the amp directly into one of the receptacles of the dedicated 20 amp circuit’s duplex receptacle outlet”

Please don’t do this without installing surge protection at your main breaker box. 

Whole house OR Zero Surge plug in.

Well....

Whole house surge protectors usually have a rather high activation voltage. 350V or so and they take time to work. On the other hand they since they are close to the ground / neutral junction they have a good chance of working well vs. using MOV strips far from the panel.  I think every home owner should invest in them, they are relatively inexpensive and placed in the right spot, but best?  Not to my mind.

Zero Surge / Brickwall clamps under 200V and has no activation time.

The best solutions IMHO are a combination whole house + series mode protection, followed by whole house + Furman.