I've noticed a lot of people using the term "app" when they really mean "mobile website." Know the difference before you hire someone to build you one.
Which is better for you? It depends on what you need.
An app is a piece of software that is downloaded to your device. Many of them have at least some functionality if your phone is offline. They're a good option if you need gamification or personalization. You can charge a fee for them. Unless it's for a very targeted group of people, you should build it for both iOS and Android compatibility.
In most cases, a mobile website is really a responsive website. You go to Helios.Media, for example, and it knows whether you're on a computer or a smartphone; the site adjusts itself. When you make updates, new features are rolled out to all visitors, without requiring them to download or update anything.
When you talk to developers about building you one of these, it's always a good idea to ask which they specialize in and which they recommend for what you need.