Use Light Ball any day. With Pikachu's 35/40/50 bulk, Eviloite won't help you at all. Especially against Pokémon Leon has, or Shielbert post game. However, doubling your Attack and Special Attack will help you against tougher trainers later in game. Additionally, with Pikachu's lousy defense stats, no stalling moves whatsoever make giving Pikachu Eviolite pretty illogical. Another point is that in game, brute force will get you wherever you need to go, so the stronger you are, the better. Also, even in competitive, I have never seen anyone run an Eviolite Pikachu. In conclusion, due to Pikachu's horrible defenses and lack of stalling moves, there is absolutely no reason to give Pikachu an Eviolite, especially where raising your Attack Stats is an option. Hope this helps!
