Magic is what makes the fantasy world what it is, and is nothing without those who are able to control magic at their will.
What name you go for will depend on you and the connotation you place behind it. For more urban fantasy, wizard/witch is used. On the other hand, high fantasy sees more use of the titles sorcerer/sorceress, or even enchanter.
For example, David Edding’s character Belgrath is called a sorcerer in his works that are high fantasy. As well in the Mercy Thompson or Harry Dresden universe, they are called witches and wizards.
The thing about magic users is that there is such a variety of them (like Necromancers) that you don’t know which to use. The best thing to do is to research they types of magic user you want to work with because each culture is different and their lore is important for that magic user to be represented properly.
Find something intriguing and use it. This is a good way to work it out if you are using the modern interpretation of a witch, which are often using a mix of different magics.