Thank you for researching Sparkling Aria and Scald for us.
Now, comparing these moves to fit Primarina:
Based on PP usage, Scald has 15pp, whereas Sparkling Aria only has 10.
Based on Power, Sparkling Aria has 90 base power, whereas Scald only has 80.
Both moves have 100 accuracy (not full, Full accuracy is —) and are in the Special category.
When Primarina holds the Waterium-Z, Sparkling Aria becomes Hydro Vortex and its base power is 175.
But, when Primarina holds the Primarium-Z, Sparkling Aria becomes Oceanic Operetta and its base power is 195.
When Primarina holds the Waterium-Z, Scald becomes Hydro Vortex and its base power is 160.
Scald can only hit a single adjacent target, but Sparkling Aria can hit all adjacent targets.
Based on this, (even though Scald has more PP than Sparkling Aria) Sparkling Aria would be the better move due to it having more power (even when Primarina uses Waterium-Z or Primarium-Z) than Scald.