Piper got annoying when all the Wyatt baby drama started ugh girls don't remind me it was just so tedious to watch
Prue showed the most facettes in her character and her power was the most effective one, too. She always saw right through to the evil's stupendous plan to destroy the Power of Three and she played the central part in each of their victories. She did NOT deserve to die such an horrible death.
I have a weakness for Paige tho. Her introduction to the show was really powerful and made me like her from the very beginning too. Maybe it's because she had that underdog-aura going with her or the fact that Rose really embodied that character and fleshed it out so that most people can identify with it.
As for favorite episodes, the Pilot was pretty perfect, From Fear to Eternity was the introduction of one of the most cruel villains Barbas and All Hell Breaks Loose is television GOLD. There have been a lot of filler episodes even in the first three seasons, but there are just as much highlights. Let me actually sleep over dat for a night until I compile my Top10 in herre.