Personally id say Magatama. Next would mood scrolls but not the meat* since those are a gamble. Just get meat* from whatever events or login bonuses. Once moods get to level 5 dont boost them anymore (Lvl 6 is 150 coupons I think) and that would be a huge waste.

Well refinement is also very much luck based especially at higher levels, same with battle armor but those two can give the biggest reward. Id recommend just using Redemption shop and other events to get refinement runes and if you want, wait till a refinement event (where you get double blessing points per attempt). Battle armor is the same way for the most part. Its really up to you, if the amount of coupons you want to spend is worth potentially losing on the gamble, where something else to gain power, like Magatama, is a sure fire, but weaker alternative.