Best way to spend your crystals?

If you are doing all three energy refreshes of both types of energy (always these first), then gear is not a bad idea. It can depend on your situation, would a 50 refresh in arena or fleet arena help you climb higher during payout to earn more crystals? Do you have a bunch of credits but need better mods, so a few 15 refreshes for the mod shop looking for good mods could be useful? Is the piece of gear you are looking at a long farm or is it a piece needed for your arena team/fleet pilots or TB/raid toons? Once you know why you want something, it makes the decision easy. And if you do not see any that seems like a good deal and none of those other options sound good right now, hoarding crystals is also fine.