You both have a point. SFM runs on a hopelessly outdated engine, it can't even do proper lighting, hasn't been updated by Valve for years because Lord GabeN doesn't care about gooners etc - it's a still good starting point to learn the ropes of animation but nothing you'll stick with forever at this point.
on the other hand, Blender...yes, it's free, regularly updated and it's not hard to make your Blender works look better than SFM. Is Blender the holy grail of 3D animation though? No, I don't think so. Industry level software like Maya which I've been looking into lately has impressed me much more than Blender ever did. The only issue here is that Maya costs $2000 per year