For 5e, I've done a Druid subclass Witch and a Wizard subclass Witch. They each covered some basics. Neither did everything. And neither offered the real breadth of archetypes different kinds/tastes of witches could be.
I played a Pathfinder Witch for quite a while, into high levels. Loved it. Loved the options. Wasn't crazy about the dependency on a familiar, but it fit some folklore/imaginings of witches and was little more than some flavor in play. Loved the supernatural "Hex" powers. Covere a lot of permutations of "witchy" type/creditted abilities.
My own homebrew is what I call a "League" class, classes that are a "league" of their own. Among other things, these are archetypes of the Class Category (Warrior, Wizard, Mystic, Rogue) that are separate and apart, their own special abilities, unique features, often an organizational affiliation in the game setting, different/multiple ability dependencies, and other mechanical differences from the Base archetypes (Fighter, Mage, Cleric, Thief), that require/deserve/delineate them as a separate class archetype.
Think of it as a "third tier" or "tertiary" class...not in "power level", certainly. But in a tree that begins with the Base "foundational" classes. Then a second "tier" of Specialist classes, those classes that are a specific kind/flavor of the Base class, usually defined with a single "special" feature that supplies features the Base class can not duplicate (or do as well): a Cavalier {fighter}, an Illusionist {mage}, etc... The League classes are the third level, branching/different archetypes from the Base classes that still fall within the Class Category. i.e. Barbarians are in the Warrior category. But they are not a "specialist" Fighter. They are their own Warrior archetype, with their own special abilities and secondary choice point to dictate the kind of Barbarian you will be.
So a Witch is a League class. There are a suite of foundational features that all witches can do. You get your spell use/list (beginning as a combo of nature magic, illusions/enchantments, some minor conjuring and transmutations), a supernatural Hex power (ranged attack to bonus/penalty to rolls), eventually potion making, and a choice of starting Witch's Crafts, and some other things.
EDIT: Here's the write-up/blurb description for my homebrewed class:
"The Witch
There are more, and more ancient, ways to harness and activate arcane energies, commune with occult powers, and produce supernatural effects than to be found in the magic tomes of mages. The Witch has access to mastering them all. Tapping into the natural world, learning secrets of dragons and titans, and opening their own powerful minds, the first witches formed the first magic-using traditions. The witch faces the challenges of adventure with a diversity of magical powers and supernatural "crafts," many unknown to even the most powerful archmage. "
/EDIT
The origins of your witchery, where you learned/began your skills/knowledge/crafts is up to the player at start of play. But by 3rd level, either by happenstance, seeking out further training, or sought after recruitment, the witch must choose a Coven to continue their advancement. I believe I originally created 3. Think we're up to 5 now. Your choice of coven expands your options for spells and dictates a series of supernatural powers that other witches and Wizard category classes can not, necessarily, know/learn.
Ex.: The witches of the Silver Moon coven gain access to more clerical spells, abjurations, etc... They can eventually channel positive energy and Turn Undead. Your "white witch" archetype. The Green Glade coven (you can probably guess) focuses more on druid/nature spells, more fae flavor: more/greater illusions and enchantments than other witches, more "fairy" witchy flavor. The coven of the Indigo Dragon involves psychic powers, raw magic/force energy spells, an eventual transmutation into draconic form, etc... There's also the Blood Flame: conjurers/demon-users, and the Ebon Eye: your general curse-uttering "wicked" witches, heavy on the shadow and necromantic magics. Considered "evil" by nearly all, including other witches/covens.
So, I think that's my favorite implementation. But I've seen a number of homebrewed or other system witches I'd love to try.