Strange Pokemon to pick for a comparison, but hmm okay.
Volcarona = completely worth your time. Come rain, wind or shine, Volcarona will be a good weather sweeper. While Hurricane isn't STAB for Volcarona, it's a good idea to have something to deal with Venusaur if you're ever facing a sun team.
Rain set:
Item: Leftovers
Ability: Flame Body
EVs: 252 HP, 200 Def, 56 Speed
Nature: Bold
- Quiver Dance
- Hurricane
- Bug Buzz
- Fiery Dance/ Substitute
Multi-use set:
Item: Life Orb
Ability: Flame Body
EVs: 252 Sp. Atk, 252 Speed, 4 HP
Nature: Timid
- Quiver Dance
- Bug Buzz
- Fiery Dance
- Giga Drain/ Roost/ HP Rock
You can only get 1 in-game. That's a testimony to how good it is; they had to limit how many you could get.
Whiscash has pretty mediocre stats, but it does have high HP. This can allow it to set up a few Dragon Dances, and then sweep effectively. However, its common typing means that it faces competitive with Gastrodon, Quagsire and Swampert, all having a x4 Grass weakness.
Still, if it can get enough DDs, it'll be able to deal with Grass types.
Whiscash @ Leftovers/ Life Orb
Ability: Hydration
EVs: 252 Atk, 252 Speed, 4 HP
Nature: Jolly
- Dragon Dance
- Earthquake
- Stone Edge
- Waterfall
Judging solely by aesthetics though, Volcarona. Whiscash looks it just realised it left the gas on and has given up on life.