In SceneVR, I represent rotations in euler angles in the markup, and then turn them to quaternions when they are parsed. This means I can lerp rotations correctly, but still use the more user-friendly euler format when expressing rotations.
I also use radians, and the default three.js euler rotation order of XYZ.
I use Eulers for rotations in the markup. In fact, it's CSS3's transform stuff and that's what they use. Internally the GLAM JS API supports either (because it's Three.js under the covers)
In SceneVR, I represent rotations in euler angles in the markup, and then turn them to quaternions when they are parsed. This means I can lerp rotations correctly, but still use the more user-friendly euler format when expressing rotations.
I also use radians, and the default three.js euler rotation order of XYZ.