The absolute best to use is a whole vanilla bean pod. In the recipe below, you’ll notice I scrape out the seeds and steep the milk and cream mixture with the vanilla pod to ensure maximum flavor. If you don’t have a vanilla bean pod, the next best bet would be to use vanilla paste so you still get those flecks of vanilla seeds. I’d recommend using about 2 teaspoons.
If you’re flavoring your ice cream with another bold flavor, like many of the customization ideas listed below, feel free to simply use vanilla extract. This is an easier and more economical option since the other ingredient will likely overpower the vanilla bean anyways.