What's the best free software to animate models? Also, is it possible to import blender model into SFM, animate it and export the animation to Unity, or back to Blender? I never used SFM but I heard it's a really good tool, so I'm wondering if I should switch.
One of the few things that Blender does well enough to really compete with top-tier software is animation. Just animate in Blender.
Also, getting models from Blender to SFM is trivially easy, but unless you plan to leave the asset there, there's no point. Use Blender Source Tools (an addon) to get your assets from Blender to SFM, if that's the route you go.