Nylon brushes are easier on bores and crowns, I still don't use them though (or very rarely). Everytime I use a brush, the accuracy diminishes until the bore gets fouled a bit. Sometimes this takes quite a few rounds, depends on the gun. I've found that if I use either Wipeout or Hoppes, the bores come out clean and accuracy along with POI doesn't change.
I should be careful that I don't say never use a brush. I think there are times when a bore may need a good scrubbing. A while back, another member challenged me to get my bore as clean as possible and then brush it. I'll have to admit that I did get a lot of carbon fouling out of it when it was brushed. It may still be a good idea for the heavily fouled barrel, but even with this, I typically only do it about twice a year.
Please don't consider me an expert on this topic. I can only tell you what is working for me. Check out this link to some good information on bore cleaning. You'll see that everyone sort of develops a technique that works for them.
Bore Brushing--How Much is Too Much?