It depends on your sector and customers. In most cases, it’s best to have both a website and an app, as it gives your customers the choice. Those who prefer websites can keep you in their bookmarks while those who prefer apps can download you to their mobile devices.
If you’re preparing to launch a business and don’t know which option to take, spend some more time researching your target demographic, as well as your competitors. Your research should tell you which option is best and will always educate you on what type of site/app to create and what features to add. You can also choose to build a mobile web app, but then you don't have the benefits of the app stores.