Best line conditioner???

They are a crap shoot. How your gear reacts to them is the unknown. Balanced power gives some gear fits. I like Furman reference 20i and I have kept it, while others have come and gone and some quick. I feel for front end gear the Harmonic Technology Magic is wonderful and one cord with a good power strip can condition your whole front end. I own 2 of these also. They don’t mess with the sound, drop the noise and open things up with tighter and deeper bass. Vocals sound natural with better presence. I have taken these cords with me to audio friends home all have purchased them used. I liked amps always better plugged into the wall. 

People have endorsed conditioners, but in all I've tried, I can't do the same.  They all change the sound but add warts that I'd rather forego

IMHO, the Furman with LiFT and SMP are the most cost effective, and most lightning proof. :)

Best,

E