I like bottle brush which is thin enough to get into narrow neck bottle. Besides, I prefer sponge bottle brush than bristle bottle brush. If I need to clean wide neck bottles, I would have wide range choice of cleaning brush. In that time, I always go for foam bottle brush.
To clean the bottom of a bottle, you need a bottle brush which has a long handle so that you can reach the bottom easily. Then you need to rotate your wrist to make the sponge head clean the bottom in 360 degree.
I think it is hard to leave no scratch when there is scale stuck on bottle. So please clean your bottle frequently. Bottle brush with sponge can do the regular cleansing. If you need to scratch something off your bottle, maybe you need some other scrubbers.