Board Thread:Questions and Answers/@comment-25294051-20150524201240/@comment-25209037-20150530211600

Crit, because it is the units that are being modified, while spark buffs modify the damage the units cause and is first applied whenever the units first spark.

Generally, offensive buff order is like this : elemental buff -> crit buff -> ATK -> spark buff. Though the first 2 can be interchanged depending on the player's preference.