There's really no comparison between AF and the others. AF is a product that people who have had a several avg. RV's buy and know what to look for.
You will find they have a lot of little extra's throughout (full size queen bed, better water pump, etc) but you will also find build details are excellent. Things like huge frames, gusseted mounting points for the suspension (never seen that in an RV before), better tires, larger wiring and cleaner construction.
Then if you actually dig into it you start finding details like more insulation and in places the others don't bother with, like all around the fridge. The seals around the slides are far tighter than any others.
The Silver fox series loads it up with other great features like double pane windows and HD shackles with wet bolts.
The list goes on but as someone who has owned and gone over lots of other brands, NW makes a great product. It could still be better but it certainly above the crowd.