Ladders what a difficult question, as I make my own. Everyone has their own preference but I dont think that the ideal brush has yet been made, it also depends on whether you do frames or not.
For the fishing poles (and also for any other system) you need lightness. So any brush that comes in below 8oz. Mine doesnt but I surform the back and sides. It can swivel round the unger alu tube and be torqued tight if wanted. Heres a Similar Bentley brush (top)
But this one is way to heavy ( they do others), the bristles pull out and the plastic backing is lousy but it does the same swivel trick.
You want bristles that are not too soft but will flex (lie down) a bit to scrub the glass a bit on their sides. Tucker used(not anymore) to make a brush with triangular Dupont filaments, that I would have liked to have seen.
I guess one of the best out there is the Salmon domestic, blue corrugated bristles that you use, the same one Gaz used to sell. But the they have a bit too many bristles to let the brush lie on the glass for my liking. I trimmed the weight to under 7 oz.
Theres a topic somewhere about brushes will see if I can find it. Coming soon are some trials I have been doing on a 3.5 oz brush that I have been using for 6 months. I am also waiting for a rumored new Vikan for WFP use (not the car brushes)
Here is one link to diy brushes on Matts site,
http://d.co.uk/phpbb/viewtopic.php?t=394&sid=5261b7cf8cad59146ac48f803225bd60