Tara MaClay, Buffy the Vampire Slayer
Tara is just my favorite character of all time. She's sweet and shy and powerful and smart. She helps the Scoobies whenever she can and however she can. In season five, she stands up to Glory to protect Dawn and the people in the park. She helps Buffy work through her stuff in season six when most of the others are piling expectations and responsibilities on her, and she keeps Buffy's secrets, telling her that it's okay to be going through what she is. Even before that, they bond when Joyce dies. And, in a later episode of season six, Tara both teases Spike on Buffy's behalf and stands up to Anya when Willow is trying to make the right decision. Tara goes from the wallflower to an independent badass without totally losing who she is or how compassionate she is. The character development happens too often in the background, and as a result she feels like a totally under-appreciated character.
Freya Mikaelson, The Originals
While Freya makes some questionable choices (see: Davina Claire), she does it all to keep her family safe. This isn't an excuse, of course, but it does make her more relatable. Also, who doesn't like to watch a super-powered witch ruin the bad guy's day? 'Cause I know I do. Also, I ship her and Keelin so hard that it's not even funny. Keelin is great and tough and smart on her own, and she also tells Freya when she's running herself into the ground with her obsessiveness and hurting herself in the process.
Vincent Griffith, The Originals
Alex/Alejandra Mortiz, Labyrinth Lost
Alex (who is technically a bruja, not a witch) makes mistakes. She's not a bad person because of it. She's human. She wants a say in how her life turns out. She just doesn't go about it in a way that initially works out. And she's not weak because of it, either. Alex is strong and loyal to her family and caring. She also gets some badass lines, like "I am an element. I am the storm" or "Right now, I'm just a girl, and there is also magic in that." (Further Labyrinth Lost love here.)
Claire, Spell on Wheels
Minerva McGonagall, Harry Potter
The badass-witch-in-residence. She's wise and kind, even if she's tough on the outside and likes to do things by the book. She stands up to Dolores Umbridge because, while McGonagall abides by rules she is more loyal to her duty to both educate and protect the students at Hogwarts and so, appropriately, she is also a leader in the Battle of Hogwarts.
Hermione Granger, Harry Potter
Smart, brave, and kind. Hermione is the witch I related to most as a kid--the know-it-all who wanted to do well in school and get ahead, sometimes at the expense of social relationships without realizing it. But, in the end, she realizes that "friendship and bravery" trump book smarts (even if the latter are super useful for, say, getting out of Devil's Snare or creating an endless bag).
Molly Weasley, Harry Potter
I'm sure that I'll realize I've forgotten about five characters once I hit "post," but so it goes. Who are your favorite witches from this list? Do you have any favs that I didn't include?