Personally season 3 is my favorite Piper season! But as far as Piper's powers go I'd say that season 5 is Piper's best season! Piper has learned how to properly blow things up without having watermelon juice on her head!

I think that season 3 is Piper's best season mainly because of the fact that Leo and her are able to overcome all of the obstacles they've had to face throughout their relationship and love story (The Elders and the whole forbidden love) and get married.

Honestly I don't know, too difficult