I think both are amazing but both are super powerful
Volcarona
Pros:
Amazing Special Attack
Solid Speed and Special Defense
6 resistances
Has access to some pretty good moves that cover it's weaknesses
Cons:
Poor Attack and Defense
4x weakness to Rock
Evolves late
Also note that Larvesta/Volcarona are only available after going through a bit of the Isle of Armor, so if you don't have the DLC, you'll need someone to trade with. commented 12 minutes ago by Giga~Blade X
Thanks, X!
Ribombee
Amazing Speed
Pretty good Special Attack
Has access to some pretty strong moves such as Psychic, Moonblast, and Bug Buzz
Bad Attack, pretty bad defense and HP
Doesn't have a large variety of coverage for it's weaknesses
Horrible Abilities
Overall, I'd pick Volcarona
If you use Volcarona, I'd suggest this moveset:
Volcarona @ anything
Ability: Flame Body
-Quiver Dance
-Fiery Dance/Fire Blast
-Bug Buzz
-Giga Drain
Hope I've helped!