Silver dragon scale mail was especially favored by folks playing
Wizards that start with a cloak of magic resistance, being thus
not affected by polymorph traps. My memories (and certainly own
preferences) have been to prefer _gray dragon scale mail_ (that
gives magic resistance and makes you safe from polymorph traps).
(There's a 50% chance that you get the reflection from Sokoban,
that's why I have a clear preference to [usually] not wish for
reflecting scale mail; random pre-Sokoban wishes almost always
go for a gray DSM.) As already implied above, if you're looking
for a role to play safely with respect to polymorph traps, play
a Wizard.
Janis