Difficult of course. Only one where you can get medium threads.

In normal you also get medium threads, however the volume is low and sometimes none.

Strange, i beat normal many times and didn't get any. I guess i just super unlucky))

I do normal, can't do difficult on auto >.

yes, you can get medium threads also in normal.
*
anyways is better to do difficult because you can buy common threads in events and monthly event and when you reach rank 4 they become useless (it's pretty easy to reach rank4) and also because medium difficulty gives less advanced clothes than difficult (and believe me you'll need a ton of them too).
but i think hidan on difficult mode is pretty annyoing since you can't go through it in any quick ways (unless you are very very very very overpowered in the BP/level ratio) while with hanzo difficult, if you are using water main, you can go on even on auto with relatively low power or complete it very easily with the sai, neji, sasuke lineup. This post was last edited by 988***@uf16 at 2017-3-31 21:25 This post was last edited by 988***@uf16 at 2017-3-31 21:26

Is it worth going for medium threads only, if you've maxed your armor level?

After rank 4 actually - no. On screen you can see how many upgrades you need. Each upgrade from 0 to 3 rank need only one thread (common ones). From 3 to 6 rank you need 5 threads (medium ones) for each upgrade. And from 7 to 9 you need 8 advanced threads for each upgrade. If my calculation is correct upgraiding it from rank 4 to 5 will take about 7-10 month.

Thanks for the info! :)