When to use rare item boosts

Is it better to use rare item boost in ultimate quests or urgent quests (with sought after drops)?

If your at the point where you getting lots of Deo weapon (around 65 plus) you can swap them in swapshop for EX cubes, then trade 6 of them for a 250 loot drop. Also 50 photon boosters (plenty come from advanced missions) can be traded for 11* weapons which also swap for EX cubes. After a bit you will have enough 250 loots to use whenever you feel. ps drooping a 250 loot will also give more photon boosters.

Here start the circle of loot.