The way I see a potential witch class, it is a class that has access to a selection of cleric, druid and warlock spells, but without most of the special abilities that those classes have. They cannot use wild shape for example, and get their powers through some sort of patron: a nature spirit, a demon, a deity. They tend to lean towards a neutral aligment of sorts, but there are pure good witches and evil hags. Some of the special abilities often given to rangers, such as an animal companion, fit the witch better I think. They would also be specialised in brewing potions, making healing salves, crafting wands and performing powerful rituals. Witches can work together in a coven to cast more powerful magic than when they are alone.