Welcome to Smogon! Take a moment to read the Introduction to Smogon for a run-down on everything Smogon, and make sure you take some time to read the global rules.
Unless you're not running Tapu Koko alongside it, Modest is the preferred nature because nothing is outspeeding A-Raichu while Electric Terrain is up outside of priority.
EDIT:
And the occasional Scarf Pheromosa.