21 drops the highest quantity per run.  It's the same rates as 20, just with a little bit more components.  There isn't a "best" stage to run for just the epic components so best practice is just to stick to what drops the most overall.

I run L21 every day on whatever faction is open.  I always have more than enough materials to forge gear whenever I need/want to.  My problem is space in the gear inventory.    

I've completed FW and run 21s every day. I only do forging during cvc, and find i typically have enough materials to do between 150-200 each of perception and resilience.

alright.  Thankyou for the insight, I will run the  highest lvl then for best results

But like I said  however I do my Forge crafting which does focus on perception gear (for my account) . I ended  up with 

10,000 basic  ingrediants / less than 1000 of the next teir ingrediant (purple border)  / and 10,000 of the highest grade  ingrediants

Sounds like you either need to forge more or do more arena for Magisteel.

You aren't forging any 4-5* gear are you?

better off only forge 5-6 for potentially worthwhile pieces, and 3-4 just for silver

My guess as well. Must have been doing 4/5 at some point to get out of whack

So just  ran lvl 21 undead and shadowkin with max keys  

result was  0 of the Epic Bloodstones  to craft  Perception

T answer some  previous  questions  here since  my last post  I have 10,000 of the steel bars  and 10,000 of the Legend Bloodstones  ...but less than 1000 of the Epic Bloodstones which are required to forge 6 star Perception

So not sure  running lvl 21  helped at all today :/   I did get some more of the Legendary Bloodstones  but already have 10K of them so not likely counted  and  some epic and  legend  forge materials  not used  in Perception gear that look like a big octagon gemstone. I am sure I seen that ingrediant in other recipies

oh well the quest continues  for me to increase the epic Bloodstone   

EDIT   actual just thought  .  wish there was a way to convert  one resource for another like a 2  for one ratio thing

VERDICT is in

I ran the 3 factions available tonight with max  crypt keys.  I chose stage 14 the second  Boss fight for this sample

All super raid runs and that stage dropped all epic crafting resources (no Legendary resources). Of the 6 super raid runs  only one did  not drop the Epic blood stones for crafting the perception 6 star gear

So I think its safe to conclude that certain stages of Faction wars do drop specific types  of crafting resources and  in order for me to build  up my epic  materials I will need to start running lower stages for a while ;)

If you run stages that low on FW, you will give up all the 5S & 6S glyphs.  IMO, it would be better to build up your supply of epic materials more slowly and still pull in the useful glyphs.  

If you just don't ever forge the 4-5 star gear, you should be fine on the materials over the long term.