0730 Primarina

Both Fast Moves feature high STAB damage output with poor energy generation, with different typing coverage. Either can be viable depending on the rest of your team composition and PvP format.

Disarming Voice is necessary regardless of which Fast Attack you choose due to it costing significantly less than Primarina's other Charged Attacks.

Charm Primarina generally prefers Hydro Pump as its secondary Charged Attack. While it is extremely expensive and doesn't synergize at all with Charm's low energy gain, it can annihilate Steel-, Fire- and Ground-type Pokemon if disrespected. Psychic can be used instead for its more realistically reachable cost and for its coverage against Poison-type Pokemon. Moonblast is an excellent move, but Primarina deals enough Fairy damage from Charm + Disarming Voice.

Waterfall Primarina deals enough Water-type damage and thus does not want Hydro Pump.

As a side note, since Primarina is a Water-type starter Pokemon, it can be anticipated to receive a Community Day in the future, which would likely result in access to the desperately needed Hydro Cannon. Fingers crossed. 

Notice that Fairy/Water typing? While this typing has done wonders for the popular Azumarill, it's not enough to save Primarina. There is a significant gap between the two Pokemon in terms of bulk, with Primarina being more fragile than most meta Pokemon. While its higher ATK stat does well for its strong Fast Move damage, the lack of energy generation, cheap Charge Moves, and shield pressure is a detriment to Primarina's performance. There's little reason to consider this Pokemon until its potential future Community Day. 

Due to the Primarina's lack of fast access to coverage options, Primarina is largely used as a single type beating stick. It can make short work of any Pokemon that's weak to its Fast Move of choice, but narrowly serves this only purpose. Tapu Fini also largely outclasses Primarina. Again, consider holding off on this Pokemon until it potentially gets its future Community Day. 

The common use of Dragon-types in this league gives Fairy Pokemon, especially those with Charm, a lot of potential. Primarina performs well in this niche partly thanks to a favorable Water secondary typing to support it. The added resistances grant Primarina superior matchups against Kyogre, Dialga, and Mamoswine compared to other Charmers. The lack of Grass and Poison Pokemon in this league eliminates a lot of threat to Primarina, making it a good consideration.