I don't like a concrete floor in a model shop because it feels too cold, sterile, industrial, unfinished-basementy...not conducive to me for doing exacting work while sitting, and feels too much like "work" work.
My last house had fairly long pile carpet in the bedroom I used for the model shop. It was comfortable and warm, but parts disappeared easily.
I have a hardwood floor in the area I model in now, and it seems ideal. Chair rolls well, wood is warm and inviting, parts don't fall into anything and get lost; though they might bounce or roll away, they're still easily rounded up, and keeping it clean is no bother, etc.