They are totally 3 different shows
Can`t compare Hex with the others because i think they made 8 season of both of them while Hex stuck with only 2.
All 3 loved to watch but i think number one is Buffy expecially with angel
and second this amazed me too Hex i prefered more the first season and part of second when still Cassie was alive.
Charmed sometimes was good but after a while i got tired of the same stuff.