Here are some common options:
* Howl: This is the most common way to spell the wolf's vocalization.
* Woo: This is a shorter and more informal spelling, often used in children's books or to describe the sound more playfully.
* A-woo-ooo: This is a more detailed spelling that tries to capture the rising and falling pitch of the wolf's howl.
* Woooo: This spelling emphasizes the prolonged nature of the sound.
Ultimately, the best spelling depends on the context and what you're trying to convey.