A well organized and to the point guide to brushes used for ski tuning, from Tognar:
It is great.
I recommend the large oval brushes - these are a little more expensive, but much better value as well... get two brass brushes: one for cleaning before waxing and one as a first brush after scraping. If you use high-fluoro waxes, then have another brass brush dedicated to that kind of wax only, otherwise you'll mix it up with the cheap stuff already embedded in the brush.
The cleaning brush is the one used most often, after filing edges and before waxing, so make sure at least that one is large oval. These are much easier to use than the little brushes - so better value when you do multiple skis.
You can then finish with a small horse hair brush. I also have large hard plastic brushes to follow up after the brass, before the horsehair. I only use the horsehair brush for race day, not regular waxing.
Careful though - the brass brushes often come in hard and soft - I prefer the harder ones.
I do own a set of rotobrushes too - they save many hours for the dad in a family of 3-4 with 3 pairs of race skis each... Horsehair rotobrushes are enough - because of the roto action, you can use them after scraping and just follow up with soft horsehair for race day. Yes - separate rotobrush for high-fluoro race wax again.
Here's a minimal but functional set of brushes for the racerkidz parent:
Free fibertex rotobrush. Once an old rotobrush dies, turn it into a fibertex power brush: clean off the old bristles and strong-glue some velcro on it. Then you will easily attach strips of fibertex (or dish cleaning pads from the dollar store) for base work on your skis...
Have fun! Read on for even more Ski Tuning Ideas.