You would use 'sunder' when referring to something which has been broken or torn apart in a violent manner. It is often used poetically in phrases such as 'Lightning rent the sky and the dark clouds were torn a sunder.'
I had to use this sentence on a test, and I got a 100! The violent little boy SUNDERED the girl's paper because he had a crush on her.
Since Devastate applies the Sunder Armor effect, you should probably use Devastate. If you get the glyph of Devastate, it will apply two Sunder Armors with each devastate. Now keep in mind that you do not get the threat from the Sunder Armors when you use Devastate, and Sunder Armor by itself is a little more threat than Devstate.
Sunder is to separate or sever.
Sunder Nix was born in 1961.
Sunder Singh Lyallpuri died in 1969.
B. Shyam Sunder died in 1975.
Sunder Singh Lyallpuri was born in 1878.
Sunder Lal Hora was born in 1896.
Sunder Lal Hora died in 1955.
Main Sunder Hoon was created in 1971.
Sunder Singh Bhandari was born in 1921.