We considered Spine. It was easy to use and enjoyable to work with. For 2D, we ended up with Maya LT exporting to Unity, not only was Maya more versatile as a 3D engine, I believe it ended up being more cost effective.
In Maya, textures were dropped onto planes, rigged, animated and exported via fbx (the pipeline was very similar to how we would have done it with Spine, with Spine exporting to JSON + Unity Runtime, while we imported the fbx directly into Unity).