Excellent insight from Greg.
My main shoe for the past two years has been a pair of XA Pro 3D, although I do a lot of "fast" trips with XC flats, and have worn out at least 6 pairs of these in the past 3 years.
I find the Salomons are a pretty good all around shoe for me; not great for any specific use, but they do a lot of things well. I have 3 pair.
XA 3D Pro size 11.5 for most of my trips.
XA 3D Pro size 13.0 for winter snow.
I also have a pair of XA Comp 4 GTX that I use in really sandy deserts in winter, where daytime highs are 50F or less.
But the one thing I hate about them is that they are slippery on steep elevations where there is a fine covering of dirt, sand, or crushed granite on the hard packed sections or a lot of larger rocks/boulders.
The past two months I have been doing these kinds of trails in Saucony Perigrines. These are the best gripping trail runners I have used. Not super light, but lighter than my Salomon's and they seem to be well constructed and tough. But time will tell.
As Greg stated, each shoe fits each person differently.