Healer plus tank buff while holding the bosses in the middle for easy spark cleaves is the best setup from my experience. Healer and tank buffs decimate all of the sparks and do massive cleave when its your turn to open the AoE boxes. DPS buff just seems "meh" (unless you want to rank, then it's pretty cool).
- - - Updated - - -
There are times when the healer or tank buff won't proc and DPS still need to kill a spark (especially if you only have one or the other). Putting the bosses in the middle to cleave them helps and eases the target swapping discomfort, but it's not an automatic fix and the fight still has a pretty decent DPS check to it.