I've seen several tutorials for creating a mobile VR app with Unity.
Some of them are using the Cardboard SDK and others are using the Google VR SDK.
What's the main difference and is there a recommendation to use one over the other?
Google VR SDK is newer and also supports the Daydream platform: https://vr.google.com/daydream/
The Google VR SDK is the latest SDK and supports new features including low-latency rendering and the new input methods.
-Tom