According to :
Much to my
surprise, when I opened the roof, I saw that all the modern NM (romex)
had the outer coating removed across most of the attic.

Out of curiousity, "modern" in the sense of being more modern than
old BX, or "modern" in the sense of being recently manufactured NM?

I've seen this (right down to the bare wire in places) too.

It was wiring within the eaves of an old house. The roof structure
(esp soffits) was heavily damaged. We assumed Racoons at the time.
Could have been mice.

[No skeletons, the soffits were that badly "not there"]

It was NM all right, but not the stuff we've been using in the past
20-30 years with thermoplastic sheath. It was the stuff from
the 40's/50's with a varnished cloth/fiber exterior sheath.

Much more appetizing to varmints than PVC, especially if the varnish
had a salty taste.

After seeing that, I will never use NM cable in a
enclosed wall or ceiling. I will use it, for example, in my garage,
where its all exposed, but if I were to ever build myself a new home,
it would be all AC, greenfield, or steel conduit. Those wires were
uninsulated for 10 feet in some spots, with only bits and pieces of
the insulation remaining. If someone had gone in the attic, they
could have been electricuted. The mouse could have started on fire
and burned the whole place.

I think this answers which is better !!!

In sofar as being chewed on by mice. On the other hand, if you were using
ground-less BX and relying on the armor sheath for grounding, having those
mice pee on the cable (they pee on _everything_) means you have poor/no ground
in very short order and a wiring fault will result in a fire or potential
electrocution.

Nothing's perfect :-(

I like TECK cable most of all. Armored cable with thermoplastic exterior
sheath, and a real ground conductor. It's what's used in hostile environments
like mineshafts, and for outdoor events, like concerts or by mobile
carnival ride companies where large quantities of people and vehicles
will be running over it.

But TECK is real expensive.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.