What's the best thing to spend my gems on?

In our opinion, the best thing to spend any free gems on is the EDF supplies chest, each one costs 300 gems, and after you have opened 10 you'll get 1 piece of excellent grade equipment.

Also check out the S Grade Supplies chest for a chance to pull S Grade equipment.

We also look in the Daily Shop for any materials or equipment that we are particularly collecting. For example, I like the Kunai weapon, so if that comes up in the daily shop, I'm buying it in order to try to upgrade it or increase it's grade.