I guess I don’t really know what’s going on with the replies, but I’ll throw in my 2c. I’ve printed with both and the guns are all still functioning so I don’t have any strength problems with either one. One major difference is that PPA is less sensitive to humidity post print and doesn’t loose strength like PA6 does. I’m not sure that matters much since for almost all applications, both of them are strong enough.

I find PPA less sensitive to moisture before printing (but you still need it DRY), easier to get nice looking prints, and less prone to warping than PA6. So overall, I prefer PPA-CF but if you have PA6 dialed in well on your printer the practical difference is negligable.