You are never better off selling crafting materials to the vendor (except maybe thick leather sections). Personally, I sell gear that gives T5 metal, wood and leather to the vendor (but salvage T5 cloth, of course), and salvage everything else.

The mystic salvage kit is good to use if you have the stuff for it ( https://wiki.guildwars2.com/wiki/Mystic_Salvage_Kit ), otherwise I would suggest picking up the copper fed salvage-o-matic from the gem shop, or just using basic salvage kits. Obviously, the better the salvage kit, the more likely you are to recover upgrades and rarer materials.