I'd go with reset=combat, for the Flame Shock.

Because, it has a fixed cooldown (even if its relatively quick), which can cause the macro or click sequence to get stuck until the spell is able to cast.

Something like Moonfire/Insect Swarm or Corruption/Immolate/Agony or the like, can be spammed over and over, as often as you'd like until you run out of mana.

But any spell with a cooldown, can get stuck and unable to cast until the cooldown ends. And that means nothing happens with the dps, until the spell goes off.