I go through the stratum of SK and usually end up with ample supplies of materials. These materials seem to go for cheap in the auction house, but I would guess in bulk they make quite a bit.
But aren't materials necessary for crafting 2* --> 3*,etc?
So, as I stated in the title, which would be the better choice?
If you plan on ragecrafting, keep everything.
A lot of the common materials dont go for much. If it isn't a shard, and you have over 80 of said material, they will not sell unless you offer them for less than 1 crown (in which case, sell em at the vendors).
However, some materials, especially the ones you can get with tokens, can sell for a lot. For example, Ghost Bells, 10 Grim Sparks, sell for about 2300 crown.
I can sell like 50 scrap metal for ~250cr. So, that would be 5cr each. It isn't worth a lot, but when you have 300 scrap metals what else are you going to do with them. Only reason to sell items like scrap metal to the vendors is if you are going to sell small quantities but then you are only getting a few crowns anyways.
I sell a lot of materials myself, but keep a good reserve. I used to sell shards, sword stones, and a few other things that went for a decent price. Used all that money to buy 4* recipes and then crafted those. I have had to re-buy a few materials, but very rarely and only after I decided I wanted to get a UV on a brandish.
My answer... figure out what you want to craft first, then sell things you really don't need now. So, for example, if you'll never make an owlite shield, then owlite features go for a decent amount.
It depends on what you want to make, as always. I never really sell my materials, unless I need cash right then, and then I only sell the stuff I am never going to use. I would save them if I were you, it would save the trouble of buying them back later if you needed them to craft.