730 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.

When using Charm, both Moonblast and Psychic require the same amount of fast moves for their initial execution despite Psychic costing less energy. It is often unlikely for Primarina to fire off multiple charge moves due to Charm's extremely poor energy generation. Moonblast can be picked for its incredible damage output, while Psychic provides coverage against Poison-type Pokemon. Hydro Pump is extremely difficult to reach due to its staggering cost, but can annihilate Fire- and Steel-type Pokemon if it is not respected.

When using Waterfall, Psychic is necessary due to its cheap cost, while Moonblast provides coverage against numerous Water-type resists. Hydro Pump is too expensive and does not provide additional coverage.

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. 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 her a good consideration.