What materials should I keep?
Have you finished crafting, or you do not plan to craft, Ascended gear? If you do, then you will need plentiful amounts of low-tier mats for those.
Because of inflation the mats might be a better way of storing value but there is risk because Anet creates new recipes that may or may not affect the value of said items without warning. You can make an educated guess and try to stockpile but if there was a clear best choice the market would have corrected for it already or will have as soon as the information were to go public.
I just sell everything since getting master crafter, only keeping around a half a stack of the uncommon things in case of new fun crafting items for personal use. Its nice having gold with nothing to spend it on sometimes when new things get released.
I keep T5/6, cooking mats, all jc-related metals, orbs, sell everything else that I’m not using, and keep stuffs for daily ascended craft.
Salvage 4 Profit + MF Guide – http://tinyurl.com/l8ff6pa
At a crafting station, go to your wardrobe and look up the following weapon types: Bandit, dredge, ogre, beaded, godskull and steam. If you think any of those weapons would look good on your character craft it.
T2-4 materials are necessary for Ascended, so if you think you are likely to go down that path then keep them.
Fine crafting materials may be of more value if upgraded, but I would have to look them up. You should look them up before selling.