If you are the one who do the animation, you probably want to use Spine, its more polished and is easier to use. Based on the development speed of unity, it could take quite a long time for them to catch up. However, it require more tricks and skills for certain visual requirement because it has its own system within unity and sometime making them talk nicely require some programming skill.
If you are also the one who do the programming, I suggest you check out what kind of visual effects or physics requirement, etc you plan to add and see if spine can satisfy your need. There are lots of question regarding how to do certain thing in this Spine-Unity forum section. You can get a glimpse about what others are currently facing and see if those are also your concern.
At the end, its more like a question whether you want to save time on doing animation or you want to save time from solving integration issues (if there is any).
