How should I ev train my piplup?

Question

I received a shiny piplup with defiant from a giveaway!
Since I have 1 legit shot to make it great, I thought to ask the experts how it should be trained. I am increasing each stat by 8 beforehand, otherwise it is untouched.

Update: It has a calm nature, with 6 for every stat besides attack (which is 5) and HP (which is 12).

Comments

Defiant calm Empoleon is pretty bad. If you have to use this Piplup, just ignore the defiant ability and give it 252 HP and 252 SpA.

---

Alternatively, you could breed it until you get an Adamant Defiant Piplup.

---

I checked its IVs and it says they're all best. Does that change anything?

---

If this is Generation 7, it doesn't change anything because IVs can be changed. By the way, according to usage stats from the high ladder, torrent Empoleon is much better than defiant Empoleon. Having an adamant nature doesn't change much.
http://www.smogon.com/stats/2017-02/moveset/gen7uu-1760.txt

Answer 1

What Astronautical and sumwun said is right. Calm Nature is bad on HA Piplup/Prinplup/Empoleon. Breed until you get a Adamant Nature and Perfect Ivs. Here's a Set and Ev Spread that Can Be good for HA Empoleon:

Empoleon @ Leftovers
Ability: Defiant
Evs: 252 Atk / 252 Hp / 6 Def
Adamant Nature (+Atk, -SpA)

Aqua Jet/Waterfall
Steel Wing
Earthquake
Swords Dance

Hope this helps :)