Smelting tipps?

My question would be, which items are worth to keep for smelting? I recall there were someone who wrote that there are some items that give better glyphs than others! Of course i get it that S grade items are better than not s grade but between regular items which ones give fhe best glyphs? Also on which level should they be smelted? Legendary or ALE? I'm curious about every type of equipment not just weapons and armors!