My most watched ones would be P3 H2O because Prue is so set on not taking comments about how she looks a lot like her mother, Give Me a Sign because it is about Prue and the struggles she goes through, and the other one with Bane because also about the focus of Prue. Those are my fav Shannen episodes.
The ones without Shannen is Hell Hath No Fury because I love all the energy Piper has in trying not to let go of Prue. Also Cheaper by the Coven because I love how the girls turn into little kids and it shows wat they were like at tht age.
These are my favorite ones the most.