Rock Guards-flap vs. brush style

[gravelcarp]

I've read quite a bit of old posts on here about rock guards, tow tectors, and trailer guards. Knowing that a trailer guard seems to be the best for protecting a boat, its a little out of range for me right now. Is there anyone with fresh info or experience that can say for sure what actually works the best? Brush or flap?? I'm guessing brush, but I have a friend who did more damage than good with a set of these. Can I get some votes on what works best? Thanks!