Which is better, a mobile app or a mobile website?

There are advantages and disadvantages for both a mobile website and a mobile application. Each typically have different audiences. You need to compare both against what you are trying to achieve.
Mobile Website

• Useful for providing quick information to customers
• Helps customers connect with businesses easily
• Provides mobile customers with a far better experience than a desktop website
• Easy to create and maintain
• Works on all operating systems

Mobile App

• Provides a better user experience
• Useful for multiple interactions with business such as viewing specials
• Useful for customers that know your brand
• More expensive than a mobile website
• Need to build a different app for each operating system (Apple’s iOS, Google Android, Windows Phone, etc)
• Needs to be downloaded through an app store