Most do but not all witches are slave to the man beast some witches like vampires splinter from the whole and try to find there own way like most outcast creatures witches are independent and solitary while others like the Glenmoril hide in small broods in caves. The ones who are solitary can choose to follow a different path depending on their preference or personal agenda and serve what ever being they choose if they choose at all...
That's a good start but remember Nocturnal also grants power limited though it may be. All daedric princes would be good but there are few that grant you power of your own symbolizing a contract has taken place or an exchange of power. A lot of other daedric princes will simply make you their champion and grant you some enchanted trinket. Is Herma Mora your favorite then?