I find it best to first optimize your toolpaths to leave as little sanding as possible, smaller stepovers for ballnose bits help alot. Also use high quality bits help as well.
As for sanding, I like to use hand sanding with sand paper, you can fold it and roll it to whatever shape you like, wrapping the pointy end of a pencil with some sand papers is a good trick.
I also like to use scrapers and metal sculpting tools used in wax and clay carving. I sharpen them up with a grinding wheel and scrape away.
I havent had much experience with flap wheels, It could work in large areas, but would probably do more harm than good in detailed carvings.