OMG this is my favorite Pokemon in SM and I'm so glad it's actually pretty usable. I'm assuming you're using Chu with Top Kek because that's where it fits the best. Here's what I use.
Raichu-Alola @ Aloraichium Z
Ability: Surge Surfer
EVs: 252 SpA / 4 SpD / 252 Spe
Modest Nature
IVs: 0 Atk
- Thunderbolt/Thunder
- Psychic/Psyshock
- Focus Blast
- Substitute/Nasty Plot/Surf/Grass Knot
So... Chu has a lot of versatility not in terms of it's actual coverage, but it's utility. If you use Thunder, obviously you use LO instead of Z-Crystal, but I like using Z-Crystal and I haven't tried the commonly dubbed stupid Pelican + Achoo + Top Kek combo. Aloraichium Z provides a surprise attack against your opponent. Normally people see that they can live a single t-bolt from Raichu and proceed to stay in and try to wall it. The Z-move lets you slap that arrogant fool with an electric surfboard to the face and show them that your apparent 3HKO is actually a 2HKO and their wall falls right over dead. This set is definitely not gonna be mainstream, but I use it because it's so incredibly unpredictable.
Thunder has uses in rain with Mr. Drizzle Pelican and would be used with life orb, but T-bolt is useful outside of rain.
Psychic ensures Raichu outputs maximum damage, but Psyshock can be used to hit physical walls like the fat pink blob we all know and love hate.
Focus Blast is good coverage alongside Psychic, although this set will commonly be spamming thunderbolts boosted by electric terrain. Focus Blast is more for hitting real big fatties who resist t-bolt and psychic.
Substitute lets you set up all over those passive losers thinking they can stop this absolute beast. Nasty Plot lets you blow up absolutely everything with even stronger thunderbolts and gives you a real Z-move nuke. Surf is better used in rain, but it lets Chu hit bulky grounds better although Grass Knot is another option that can work outside of rain if you don't feel you need the utilities of sub or NP.
I'm all up for criticism, but this is my take on what I think is a fantastic Pokemon.